Refactor descriptor handling and shader compilation

Refactored descriptor allocation and release logic by introducing `IDescriptorAllocator` and replacing `DescriptorHeapAllocator` with `D3D12DescriptorHeap`. Updated descriptor structs to include validation properties and improved memory management with `ReadOnlySpan`.

Enhanced shader compilation by introducing `ShaderStage` and `CompilerVersion` enums, enabling more flexible and maintainable shader handling.

Refactored `Mesh` to use `IBuffer` for vertex and index buffers, added bindless descriptor support, and improved resource cleanup.

Updated `RenderSystem` and other components for better initialization, error handling, and disposal logic. General improvements to code readability and maintainability.

Ghost.Graphics/D3D12/D3D12CommandBuffer.cs

@@ -117,6 +117,7 @@ internal unsafe class D3D12CommandBuffer : ICommandBuffer
         throw new NotImplementedException();
     }
 
+    // TODO: Batch draw calls by material to minimize state changes
     public void DrawMesh(Mesh mesh, Material material)
     {
         // Bind the bindless material (sets up root signature, pipeline state, and descriptor heaps)