[Bug] Android IL2CPP build fails: UnityLinker can’t resolve BouncyCastle.Cryptography with v1.2.9

**Bug summary**
After install v1.2.9, Android IL2CPP builds consistently fail during the Unity CIL Linker step with an assembly resolution error for BouncyCastle.Cryptography (2.x). Unity can’t find that assembly even when I add the DLL manually.

Error log (Editor.log excerpt)
`Building Library\Bee\artifacts\Android\ManagedStripped failed with output:
D:\Unity\Hub\Editor\6000.1.8f1\Editor\Data\il2cpp\build\deploy\UnityLinker.exe @Library\Bee\artifacts\rsp\16162982357633868796.rsp
Fatal error in Unity CIL Linker
Mono.Cecil.AssemblyResolutionException: Failed to resolve assembly: 'BouncyCastle.Cryptography, Version=2.0.0.0, Culture=neutral, PublicKeyToken=null'
at Unity.IL2CPP.Common.MissingMethodStubber.GetTypeModule(...)
at Unity.Linker.Steps.AddUnresolvedStubsStep.MarkAssemblyOfType(...)
at Unity.Linker.Steps.Marking.UnresolvedStubMarking.HandleUnresolvedType(...)
...
UnityEditor.EditorApplication:Internal_CallDelayFunctions ()
`

**To Reproduce**
1. Create a new Unity project (Unity 6000.1.8f1).
2. Add Solana.Unity-SDK v1.2.9 via Package Manager (Git URL).
3. Switch to Android, set IL2CPP / ARM64.
4. Build → Linker fails with Failed to resolve assembly: 'BouncyCastle.Cryptography, Version=2.0.0.0'.

**Expected behavior**
Android IL2CPP build succeeds (the SDK resolves its crypto dependency without manual intervention).

**Unity versions tested**
-6000.1.8f1 (primary)
-6000.2.7f2 (also repros)

**Platform / Build settings:**
-Target: Android
-Scripting Backend: IL2CPP
-Architecture: ARM64
-Managed Stripping Level: (tried Low/Medium)
-OS: Windows

**Additional context**
Even with BouncyCastle.Cryptography.dll (2.x, netstandard2.0) present and enabled for Android, the .rsp used by UnityLinker appears to omit the 2.x DLL (linker still reports it missing)

Reproduce the failure in a Unity 6000.1.8f1 project using Solana.Unity-SDK v1.2.9, Android, IL2CPP, and ARM64. Inspect the package dependency configuration and generated UnityLinker .rsp to determine why BouncyCastle.Cryptography 2.x is omitted; done means the Android IL2CPP build succeeds without manually adding the DLL.

Written by the indexing model from the issue text.