Refactor RenderGraph barrier/state tracking system

Major overhaul of resource barrier and state tracking in RenderGraph:
- Introduce ResourceBarrierData for explicit (layout, access, sync) tracking.
- Separate aliasing and transition barriers; explicit aliasing support.
- Remove BufferHint; infer buffer usage from BufferUsage flags.
- Update TextureAccess/BufferAccess to include usage requirements.
- Improve enums (BarrierSync, BarrierAccess, BarrierLayout) for D3D12 alignment.
- Update D3D12CommandBuffer to use new barrier data and error handling.
- Make D3D12DescriptorHeap a class; add ReleaseSampler to IResourceDatabase.
- Reset resource pools and aliasing managers each frame.
- Batch and flush barriers efficiently per pass.
- Update HLSL mesh shader macros to [NumThreads].
- Remove obsolete code and improve documentation.
This refactor improves correctness, extensibility, and prepares for advanced features.

Ghost.Graphics/D3D12/D3D12ResourceDatabase.cs

@@ -323,6 +323,15 @@ internal class D3D12ResourceDatabase : IResourceDatabase
         return _samplers.TryGetValue(desc, out id);
     }
 
+    public void ReleaseSampler(Identifier<Sampler> id)
+    {
+        ObjectDisposedException.ThrowIf(_disposed, this);
+
+        // NOTE: We almost never release samplers individually, because they are cheap and can be reused.
+        // Ideally we would release all samplers at once when disposing the ResourceDatabase.
+        _descriptorAllocator.Release(new Identifier<SamplerDescriptor>(id.Value));
+    }
+
     public Handle<Mesh> AddMesh(ref readonly Mesh mesh)
     {
         ObjectDisposedException.ThrowIf(_disposed, this);