Upgrade to .net9

Infra/Buffers/ImmovableMemory.cs

@@ -0,0 +1,37 @@
+using System.Buffers;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+
+namespace StitchATon2.Infra.Buffers;
+
+internal sealed unsafe class ImmovableMemory<T> : MemoryManager<T> where T : unmanaged
+{
+    private readonly T* _pointer;
+    private readonly int _length;
+    private bool _disposed;
+
+    public ImmovableMemory(int count)
+    {
+        _pointer = (T*)NativeMemory.Alloc((nuint)count, (nuint)Unsafe.SizeOf<T>());
+        _length = count;
+    }
+    
+    protected override void Dispose(bool disposing)
+    {
+        if (!_disposed)
+        {
+            NativeMemory.Free(_pointer);
+            _disposed = true;
+        }
+    }
+
+    public override Span<T> GetSpan()
+        => new(_pointer, _length);
+
+    public override MemoryHandle Pin(int elementIndex = 0)
+        => new(_pointer + elementIndex);
+
+    public override void Unpin()
+    {
+    }
+}