feat(graphics): refactor pipeline keying and allocators

Major refactor of graphics pipeline keying, shader cache, and resource allocation.
Replaced most Allocator usage with AllocationHandle, modernized logger usage,
and unified pipeline state keys. Updated MeshUtility to use AllocationHandle.FreeList.
Added new shader pipeline architecture docs and improved error handling throughout.

BREAKING CHANGE: Pipeline keying and resource allocation APIs have changed.

src/Runtime/Ghost.Graphics.RHI/RootSignatureLayout.cs

@@ -14,7 +14,7 @@ public static class RootSignatureLayout
 public struct PushConstantsData
 {
     public const uint NUM_32BITS_VALUE = 12u / sizeof(uint);
-    
+
     [FieldOffset(0)]
     public uint frameBuffer;
     [FieldOffset(4)]
@@ -23,6 +23,11 @@ public struct PushConstantsData
     public uint instanceIndex;
     [FieldOffset(8)]
     public uint propertyBuffer;
+
+    public ReadOnlySpan<uint> AsUInts()
+    {
+        return MemoryMarshal.CreateReadOnlySpan(ref frameBuffer, (int)NUM_32BITS_VALUE);
+    }
 }
 
 [StructLayout(LayoutKind.Sequential)]