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/Contracts/IAllocator.cs

@@ -0,0 +1,52 @@
+using Misaki.HighPerformance.LowLevel.Collections;
+
+namespace Misaki.HighPerformance.LowLevel.Contracts;
+
+using unsafe AllocFunc = delegate* unmanaged<void*, nuint, nuint, AllocationOption, void*>;
+using unsafe FreeFunc = delegate* unmanaged<void*, void*, void>;
+using unsafe ReallocFunc = delegate* unmanaged<void*, void*, nuint, nuint, void*>;
+
+public unsafe readonly struct AllocationHandle
+{
+    public void* Allocator
+    {
+        get;
+    }
+
+    public AllocFunc Alloc
+    {
+        get;
+    }
+
+    public ReallocFunc Realloc
+    {
+        get;
+    }
+
+    public FreeFunc Free
+    {
+        get;
+    }
+
+    public AllocationHandle(void* allocator, AllocFunc alloc, ReallocFunc realloc, FreeFunc free)
+    {
+        Allocator = allocator;
+        Alloc = alloc;
+        Realloc = realloc;
+        Free = free;
+    }
+}
+
+/// <summary>
+/// Represents an allocator interface for managing memory allocations.
+/// </summary>
+/// <remarks>
+/// The allocator must be static or pined to a specific memory region.
+/// </remarks>
+public unsafe interface IAllocator
+{
+    public ref AllocationHandle Handle
+    {
+        get;
+    }
+}