feat(allocator): add VirtualArena and FreeList allocators

Introduce VirtualArena for large, thread-safe virtual memory allocation and FreeList allocator for efficient persistent allocations. Update AllocationManager to support new allocators, add cross-platform virtual memory utilities, and improve thread-safety and performance in existing allocators. Bump version to 1.5.0 and update project configuration.

BREAKING CHANGE: AllocationManager initialization now requires explicit parameters for arena and FreeList capacities. Existing allocator usage may require code changes.

Misaki.HighPerformance.LowLevel/Buffer/Stack.cs

@@ -221,6 +221,11 @@ public unsafe partial struct Stack : IDisposable
 
     public void Dispose()
     {
+        if (_buffer == null)
+        {
+            return;
+        }
+
         Free(_buffer);
 
         _buffer = null;