Swift modelgen creates wrong decoding initializer with optional custom type in required arra

### Environment information

```plain text
System:
OS: macOS 15.1
CPU: (12) arm64 Apple M3 Pro
Memory: 123.80 MB / 36.00 GB
Shell: /bin/zsh
Binaries:
Node: 22.9.0 - /opt/homebrew/bin/node
Yarn: undefined - undefined
npm: 10.8.3 - /opt/homebrew/bin/npm
pnpm: undefined - undefined
NPM Packages:
@aws-amplify/auth-construct: 1.3.0
@aws-amplify/backend: 1.2.1
@aws-amplify/backend-auth: 1.1.4
@aws-amplify/backend-cli: 1.2.6
@aws-amplify/backend-data: 1.1.3
@aws-amplify/backend-deployer: 1.1.2
@aws-amplify/backend-function: 1.4.0
@aws-amplify/backend-output-schemas: 1.2.0
@aws-amplify/backend-output-storage: 1.1.1
@aws-amplify/backend-secret: 1.1.1
@aws-amplify/backend-storage: 1.1.2
@aws-amplify/cli-core: 1.1.2
@aws-amplify/client-config: 1.3.0
@aws-amplify/deployed-backend-client: 1.4.0
@aws-amplify/form-generator: 1.0.1
@aws-amplify/model-generator: 1.0.6
@aws-amplify/platform-core: 1.1.0
@aws-amplify/plugin-types: 1.2.1
@aws-amplify/sandbox: 1.2.1
@aws-amplify/schema-generator: 1.2.2
aws-amplify: 6.6.0
aws-cdk: 2.158.0
aws-cdk-lib: 2.158.0
typescript: 5.6.2
AWS environment variables:
AWS_STS_REGIONAL_ENDPOINTS = regional
AWS_NODEJS_CONNECTION_REUSE_ENABLED = 1
AWS_SDK_LOAD_CONFIG = 1
No CDK environment variables
```

### Describe the bug

When running `npx ampx generate graphql-client-code --format modelgen --model-target swift` on my Amplify Swift project, depending on the models defined in `data/resource.ts` the decoding initializer does not compile due to a `Cannot assign value of type '[MyCustomType]?' to type '[MyCustomType?]` error in Xcode.

### Expected Behavior

`myCustomTypes = try values.decode([MyCustomType?].self, forKey: .myCustomTypes)` should be generated

### Current Behavior

`myCustomTypes = try? values.decode([MyCustomType].self, forKey: .myCustomTypes)` is generated

### Reproduction steps

Define the following models in `data/resource.ts`:
```
// Custom types

MyCustomType: a.customType({
context: a.string(),
}),

// Models

MyModel: a.model({
context: a.string(),
myCustomTypes: a.ref('MyCustomType').array().required(),
myOtherModelId: a.id().required(),
myOtherModel: a.belongsTo('MyOtherModel', 'myOtherModelId')
})
.authorization(allow => [allow.owner()]),

MyOtherModel: a.model({
context: a.string(),
myModel: a.hasOne('MyModel', 'myOtherModelId')
})
.authorization(allow => [allow.owner()]),
```

And run `npx ampx generate graphql-client-code --format modelgen --model-target swift` to create the models.

### Additional Information/Context

When changing the custom type in the array to a non-optional, the decoding is done correctly.
```
// Custom types

MyCustomType: a.customType({
context: a.string(),
}),

// Models

MyModel: a.model({
context: a.string(),
myCustomTypes: a.ref('MyCustomType').required().array().required(), // <-- changed !!!
myOtherModelId: a.id().required(),
myOtherModel: a.belongsTo('MyOtherModel', 'myOtherModelId')
})
.authorization(allow => [allow.owner()]),

MyOtherModel: a.model({
context: a.string(),
myModel: a.hasOne('MyModel', 'myOtherModelId')
})
.authorization(allow => [allow.owner()]),
```

### Environment details (OS name and version, etc.)

macOS 15.1, Xcode 16.1 beta 2, swift-tools-version: 6.0, swiftLanguageModes v5