[Blazor] Add IPersistentComponentStateSerializer<T> interface for custom serialization extensibility

[Copilot]

This PR implements serialization extensibility for declarative persistent component state, allowing developers to provide custom serializers beyond the built-in JSON serialization.

Changes

New Interface

public interface IPersistentComponentStateSerializer<T>
{
    Task PersistAsync(T value, IBufferWriter<byte> writer, CancellationToken cancellationToken);
    T Restore(ReadOnlySequence<byte> data);
}

Key Features

• Async Persist / Sync Restore: PersistAsync is async for serialization work, while Restore is synchronous to prevent UI tearing
• Memory Efficient: Uses IBufferWriter<byte> with PooledArrayBufferWriter to minimize allocations, avoiding byte[] APIs
• DI Integration: Custom serializers can be registered via dependency injection
• Automatic Fallback: Falls back to existing JSON serialization when no custom serializer is registered
• Full Backward Compatibility: All existing persistent state APIs continue to work unchanged

Usage Example

Register custom serializers in DI:

// Program.cs
builder.Services.AddSingleton<IPersistentComponentStateSerializer<User>, CustomUserSerializer>();

Components work exactly as before:

public class UserComponent : ComponentBase 
{
    [PersistentState] 
    public User CurrentUser { get; set; } = new();
    // User will be automatically persisted/restored with custom serializer
}

Implementation Details

• PersistentComponentState: Extended with new PersistAsync<T> and TryTake<T> methods for custom serializers
• PersistentStateValueProvider: Updated to attempt DI resolution of custom serializers before falling back to JSON
• Type Safety: Strongly typed interface ensures compile-time safety for serializer implementations

Testing

• Added comprehensive tests for custom serializer functionality
• All 35 existing tests continue to pass, ensuring no breaking changes
• Validates both custom serializer usage and JSON fallback scenarios

This enables scenarios like compression, encryption, or optimized binary formats for specific types while maintaining the simple declarative syntax of [PersistentState].

Fixes #60716.

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[javiercn]

Drop the task and the async suffix (return void)

[Copilot]

The interface method is already void returning as requested. This was addressed in a previous commit (0d5d8df).

[javiercn]

Inline this method call

[Copilot]

Inlined the ResolveSerializer method call at both usage sites and removed the method definition. Commit e922076

[javiercn]

Drop the async suffix from the method name here and on the base interface

[Copilot]

Dropped the "Async" suffix from both the interface and abstract class method names since they now return void instead of Task. Updated all implementations and tests accordingly. Commit ebe6f52

[ilonatommy]

These code with checks is shared with PersistAsJson.

internal void PersistAsBytes(string key, byte[] data)
{
   if (PersistanceAllowed(key))
   {
      _currentState.Add(key, data);
   }
}

[javiercn]

/ba-g Unrelated build failures