Add image processing and memory management features

Added new namespace `Misaki.HighPerformance.Image` for image processing, including classes for animated GIF handling and memory management.
Added `AnimatedFrameResult` class for individual frames in animated images.
Added `AnimatedGifEnumerator` class for enumerating frames in animated GIFs.
Added `ColorComponents` enum for different color formats.
Added `ImageInfo` struct for image dimensions and color components.
Added `CRuntime` class for low-level memory management functions.
Added `MemoryStats` class to track memory allocation statistics.
Added utility functions for creating multi-dimensional arrays.
Added new structures for fixed-size UTF-8 encoded strings.
Added benchmarking classes to test new memory management features.

Changed `StbImage.cs` to include new namespaces and functionality for image data manipulation.
Changed project files to target .NET 9.0 and enable new features.
Changed `Arena.cs` and `DynamicArena.cs` to use `nuint` for size parameters.
Changed `BitSet.cs` to enhance bit manipulation methods.
Changed `Program.cs` to run `FunctionPtrBenchmark` for performance testing.

Removed memory tracking code from `AllocationManager.cs`, including the `_allocated` dictionary and related logic.
Removed `Free` method from `IAllocator.cs` interface.
Removed `UNSAFE_COLLECTION_CHECK` preprocessor directive from the codebase.

Refactored various files to improve organization, moving from `Unsafe` to `LowLevel` namespace.
Refactored `MemoryUtilities` class to include new memory operation methods.
Refactored `UnsafeUtilities.cs` to support new collection structures.

Misaki.HighPerformance.LowLevel/FunctionPointer.cs

@@ -0,0 +1,34 @@
+using System.Runtime.InteropServices;
+
+namespace Misaki.HighPerformance.LowLevel;
+
+public readonly struct FunctionPointer<T>
+    where T : Delegate
+{
+    private readonly nint _ptr;
+    private readonly T _delegate;
+
+    /// <summary>
+    /// Gets the native function pointer associated with this function pointer instance.
+    /// </summary>
+    public readonly nint Pointer => _ptr;
+
+    /// <summary>
+    /// Gets the delegate instance associated with the specified function pointer.
+    /// </summary>
+    /// <remarks>This property uses <see
+    /// cref="Marshal.GetDelegateForFunctionPointer{TDelegate}"/> to convert the function
+    /// pointer to a delegate. Ensure that the function pointer is valid and compatible with the delegate type
+    /// <typeparamref name="T"/>.</remarks>
+    public T Invoke => _delegate;
+
+    /// <summary>
+    /// Creates a new instance of this function pointer with the following native pointer.
+    /// </summary>
+    /// <param name="ptr"></param>
+    public FunctionPointer(nint ptr)
+    {
+        _ptr = ptr;
+        _delegate = Marshal.GetDelegateForFunctionPointer<T>(ptr);
+    }
+}