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.Test/FunctionPtrBenchmark.cs

@@ -0,0 +1,47 @@
+using BenchmarkDotNet.Attributes;
+using Misaki.HighPerformance.LowLevel;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+
+namespace Misaki.HighPerformance.Test;
+
+[MemoryDiagnoser]
+public unsafe class FunctionPtrBenchmark
+{
+    private delegate float FunctionPointerDelegate(float a, float b);
+
+    private float _sink;
+
+    private FunctionPointer<FunctionPointerDelegate> _addManaged;
+    private delegate* unmanaged<float, float, float> _addUnmanaged;
+
+    public FunctionPtrBenchmark()
+    {
+        _addManaged = new(Marshal.GetFunctionPointerForDelegate<FunctionPointerDelegate>(Add));
+        _addUnmanaged = &AddUnmanaged;
+    }
+
+    private float Add(float a, float b)
+    {
+        return a + b;
+    }
+
+    [UnmanagedCallersOnly]
+    private static float AddUnmanaged(float a, float b)
+    {
+        return a + b;
+    }
+
+    [Benchmark(Baseline = true)]
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    public void InvokeManaged()
+    {
+        _sink = _addManaged.Invoke(1.0f, 2.0f);
+    }
+
+    [Benchmark]
+    public void InvokeUnmanaged()
+    {
+        _sink = _addUnmanaged(1.0f, 2.0f);
+    }
+}