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/Collections/AllocationOption.cs

@@ -0,0 +1,38 @@
+namespace Misaki.HighPerformance.LowLevel.Collections;
+
+[Flags]
+public enum AllocationOption : byte
+{
+    None = 0,
+    /// <summary>
+    /// Allocator for initialized memory.
+    /// </summary>
+    Clear = 1 << 0,
+    /// <summary>
+    /// Allocator for untracked memory. It always allocates memory without using the allocation manager.
+    /// Always free it manually even if you use the <see cref="Allocator.Temp"/> allocator.
+    /// </summary>
+    /// <remarks>
+    /// Use this option carefully, as the allocation manager will not track the memory.
+    /// No warning will be given if the memory is not freed.
+    /// </remarks>
+    UnTracked = 1 << 1,
+}
+
+public enum Allocator : byte
+{
+    // Make the first allocator as invalid because we don't want to user create a default collection without passing any parameters
+    Invalid,
+    /// <summary>
+    /// Allocator for temporary allocations. Allocations are cleared after use.
+    /// </summary>
+    Temp,
+    /// <summary>
+    /// Allocator for persistent allocations. Allocations are not cleared after use.
+    /// </summary>
+    Persistent,
+    /// <summary>
+    /// Allocator for external memory. Allocations are not cleared after use.
+    /// </summary>
+    External
+}