[Az.DataProtection 3.0.0] Initialize-AzDataProtectionBackupInstance throws "Cannot convert System.Object[] to IDataStoreParameters" for TrustedLaunch OS disks

### Description

`Initialize-AzDataProtectionBackupInstance -DatasourceType AzureDisk` throws an internal cast exception when invoked against a TrustedLaunch OS disk (Premium SSD LRS). The exception originates inside the cmdlet during construction of the `DataStoreParametersList` property, **before the cmdlet returns**, so no client-side workaround is available.

```
Exception setting "DataStoreParametersList": "Cannot convert the
"System.Object[]" value of type "System.Object[]" to type
"Microsoft.Azure.PowerShell.Cmdlets.DataProtection.Models.IDataStoreParameters"."
```

Both documented invocation patterns fail identically:

1. **Post-mutation pattern** (per the MS Learn example): call `Initialize-*` without `-SnapshotResourceGroupId`, then mutate `$instance.Property.PolicyInfo.PolicyParameter.DataStoreParametersList[0].ResourceGroupId`. The exception is thrown by `Initialize-*` itself, so the post-mutation line is never reached.
2. **Parameter pattern**: pass `-SnapshotResourceGroupId` directly to `Initialize-*`. The same exception is thrown at the same line — passing the parameter does not bypass the broken default-construction code path.

Standard managed disks (non-TrustedLaunch) in the same subscription and the same vault initialize successfully with both patterns. The error appears to be specific to disks belonging to a TrustedLaunch VM.

### Expected behavior

`Initialize-AzDataProtectionBackupInstance -DatasourceType AzureDisk` should return an initialized `IBackupInstanceResource` for a TrustedLaunch OS disk, the same way it does for Standard SSD / Premium SSD disks attached to non-TrustedLaunch VMs. Azure Disk Backup explicitly supports Azure managed disks (Standard HDD, Standard SSD, Premium SSD, Premium SSD v2, Ultra) per https://learn.microsoft.com/azure/backup/disk-backup-support-matrix **without any TrustedLaunch carve-out**.

### Actual behavior

The same call against a non-TrustedLaunch Premium SSD disk in the same vault and subscription succeeds and returns a valid `IBackupInstanceResource`. The TrustedLaunch disk consistently and deterministically throws the cast exception above.

### Disk details (target of the failing call)

| Property | Value |
|---|---|
| Storage type | Premium SSD LRS |
| Disk state | Attached |
| OS type | Windows |
| VM generation | V2 |
| **Security type** | **Trusted Launch** |
| Disk size | 127 GiB |
| Max shares | 0 |

### Hypothesis / observation

The exception text indicates the cmdlet is constructing `DataStoreParametersList` as `System.Object[]` and failing to assign it to a strongly-typed `IDataStoreParameters` property on the model object. This looks like a manifest / default-construction path that handles the TrustedLaunch case differently from the standard disk case and produces an untyped array where a typed one is expected.

The MS Learn doc page for `Initialize-AzDataProtectionBackupInstance` instructs users to mutate `DataStoreParametersList[0].ResourceGroupId` post-call — implying the cmdlet is meant to return a model with that property already constructed and typed. For the TrustedLaunch disk, the cmdlet never returns because the construction itself fails.

### Workaround currently in use

We are detecting this specific error signature (`DataStoreParametersList` + `IDataStoreParameters`) in PowerShell and skipping the disk for the run with a single `[WARN]` log line. On non-TrustedLaunch disks the script proceeds normally. This workaround is fragile across module updates because it relies on exception string matching.

### Impact

- All TrustedLaunch VMs in our environment cannot have their OS or data disks protected via Az.DataProtection until this is resolved.
- The same code path succeeds for thousands of non-TrustedLaunch managed disks in the same subscription across the same nightly automation run — failure is specific to TrustedLaunch.
- Workaround in PowerShell scripts requires special-casing TrustedLaunch disks via exception string matching, which is fragile across module updates.

### Issue script & Debug output

```PowerShell
$DebugPreference = 'Continue'

# Repro environment:
# PowerShell 5.1 (Windows ConsoleHost), Az.DataProtection 3.0.0
# Disk: TrustedLaunch OS disk, Premium SSD LRS

$sub = ''
$diskRG = ''
$diskName = ''
$vaultRG = ''
$vault = ''
$policy = ''

$policyId = "/subscriptions/$sub/resourceGroups/$vaultRG/providers/Microsoft.DataProtection/backupVaults/$vault/backupPolicies/$policy"
$diskId = "/subscriptions/$sub/resourceGroups/$diskRG/providers/Microsoft.Compute/disks/$diskName"

# ---------------------------------------------------------------------------
# Attempt 1: post-mutation pattern (the documented MS Learn example).
# ---------------------------------------------------------------------------
$instance = Initialize-AzDataProtectionBackupInstance `
-DatasourceType AzureDisk `
-DatasourceLocation `
-PolicyId $policyId `
-DatasourceId $diskId

# ^ Throws here for TrustedLaunch OS disks; post-mutation line below is never reached.
$instance.Property.PolicyInfo.PolicyParameter.DataStoreParametersList[0].ResourceGroupId = `
"/subscriptions/$sub/resourceGroups/$vaultRG"

# ---------------------------------------------------------------------------
# Attempt 2: parameter pattern (pass -SnapshotResourceGroupId directly).
# Hypothesis was that passing the parameter would bypass default construction;
# in practice it throws the IDENTICAL exception at the same line.
# ---------------------------------------------------------------------------
$instance = Initialize-AzDataProtectionBackupInstance `
-DatasourceType AzureDisk `
-DatasourceLocation `
-PolicyId $policyId `
-DatasourceId $diskId `
-SnapshotResourceGroupId "/subscriptions/$sub/resourceGroups/$vaultRG"

# ^ Same exception. Both attempts fail before Initialize-* returns.

**Resulting exception (identical for both attempts):**

Exception setting "DataStoreParametersList": "Cannot convert the
"System.Object[]" value of type "System.Object[]" to type
"Microsoft.Azure.PowerShell.Cmdlets.DataProtection.Models.IDataStoreParameters"."
At line:1 char:1
+ $instance = Initialize-AzDataProtectionBackupInstance @params
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : NotSpecified: (:) [], SetValueInvocationException
+ FullyQualifiedErrorId : ExceptionWhenSetting

**Params dict (Attempt 2, anonymized) from the wrapping automation log:**

{
"DatasourceType": "AzureDisk",
"DatasourceLocation": "",
"PolicyId": "/subscriptions//resourceGroups//providers/Microsoft.DataProtection/backupVaults//backupPolicies/",
"DatasourceId": "/subscriptions//resourceGroups//providers/Microsoft.Compute/disks/",
"SnapshotResourceGroupId": "/subscriptions//resourceGroups/"
}
```

### Environment data

```PowerShell
Name Value
---- -----
PSVersion 5.1.20348.4294
PSEdition Desktop
PSCompatibleVersions {1.0, 2.0, 3.0, 4.0...}
BuildVersion 10.0.20348.4294
CLRVersion 4.0.30319.42000
WSManStackVersion 3.0
PSRemotingProtocolVersion 2.3
SerializationVersion 1.1.0.1

Host: Windows Server 2022 — Azure App Service WebJob (non-interactive `ConsoleHost`). Repro also observed on Windows Server 2019 in PowerShell ISE.

Authentication: Managed Identity (App Service) and interactive (ISE) — both reproduce identically.
```

### Module versions

```PowerShell
ModuleType Version Name ExportedCommands
---------- ------- ---- ----------------
Script 5.5.0 Az.Accounts {Add-AzEnvironment, Clear-AzConfig, Clear-AzContext...}
Script 11.6.0 Az.Compute {Add-AzImageDataDisk, Add-AzVhd, Add-AzVMAdditionalUnattendContent...}
Script 3.0.0 Az.DataProtection {Backup-AzDataProtectionBackupInstanceAdhoc, Edit-AzDataProtectionPolicyRetentionRuleClientObject, Edit-AzDataProtectionPolicyTagClientObject...}
Script 6.5.0 Az.KeyVault {Add-AzKeyVaultCertificate, Add-AzKeyVaultKey, Add-AzKeyVaultManagedHsmRegion...}
Script 7.12.0 Az.RecoveryServices {Backup-AzRecoveryServicesBackupItem, Copy-AzRecoveryServicesVault, Disable-AzRecoveryServicesBackupAutoProtection...}
Script 1.3.0 Az.ResourceGraph {Search-AzGraph}
Script 10.0.0 Az.Resources {Add-AzADGroupMember, Export-AzResourceGroup, Get-AzADAppCredential...}

`Az` rollup: **16.0.0** (June 2026).
```

### Error output

```PowerShell
HistoryId:

Exception : Exception setting "DataStoreParametersList": "Cannot convert
the "System.Object[]" value of type "System.Object[]" to type
"Microsoft.Azure.PowerShell.Cmdlets.DataProtection.Models.IDataStoreParameters"."
InvocationInfo :
MyCommand : Initialize-AzDataProtectionBackupInstance
Line : $instance = Initialize-AzDataProtectionBackupInstance @params
PositionMessage : At line:1 char:1
+ $instance = Initialize-AzDataProtectionBackupInstance @params
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
CategoryInfo : NotSpecified: (:) [], SetValueInvocationException
FullyQualifiedErrorId: ExceptionWhenSetting
ScriptStackTrace :
at Initialize-AzDataProtectionBackupInstance, <...>\Az.DataProtection\3.0.0\Az.DataProtection.psm1
(within the cmdlet's default-construction path for DataStoreParametersList)
PSMessageDetails :

**Reproduces deterministically** for the TrustedLaunch disk on every invocation. The same `Initialize-AzDataProtectionBackupInstance` call against any non-TrustedLaunch managed disk in the same subscription, vault, and policy returns a valid `IBackupInstanceResource` without error.
```

Start with the Az.DataProtection\3.0.0\Az.DataProtection.psm1 implementation of Initialize-AzDataProtectionBackupInstance, specifically its default-construction path for DataStoreParametersList. Compare construction for TrustedLaunch and non-TrustedLaunch managed disks, then verify both documented invocation patterns and confirm the cmdlet returns a valid IBackupInstanceResource without the IDataStoreParameters cast exception.

Written by the indexing model from the issue text.