Refactor memory management and improve allocation APIs

Updated `ReallocFunc` to support `oldSize`, `newSize`, and `AllocationOption`, enabling more granular control over memory reallocation. Simplified `AllocationInfo` by removing the `FreeHandler` property. Enhanced `Reallocate` and `Allocate` methods in `AllocationManager` to handle memory clearing and tracking more effectively.

Refactored `UnsafeSparseSet` to use `UnsafeArray<T>` directly, added a `generations` array, and replaced the `freeList` with `UnsafeStack<int>` for better performance and simplicity. Updated `Resize`, `Add`, and `Remove` methods to improve memory handling and code clarity.

Introduced `AllocationOption` support in `Resize` methods across `IUnsafeCollection` implementations for flexible resizing behavior. Added `GetUnsafePtr` extension methods in `UnsafeUtilities` for direct access to span data.

Added new tests for `UnsafeSparseSet` to validate resizing, clearing, enumeration, and memory compaction. These changes improve memory management, enhance performance, and ensure correctness.

Misaki.HighPerformance.LowLevel/Collections/UnsafeHashMap.cs

@@ -184,7 +184,7 @@ public unsafe struct UnsafeHashMap<TKey, TValue> : IUnsafeCollection<KeyValuePai
     /// </summary>
     public void TrimExcess() => _hashMap.TrimExcess();
 
-    public void Resize(int newSize)
+    public void Resize(int newSize, AllocationOption option = AllocationOption.None)
     {
         _hashMap.Resize(newSize);
     }