Update memory management and collection structures

Added `AllocationHandler` struct for memory allocation management.
Added `UnsafeArrayPool` class for pooling `UnsafeArray<T>` instances.
Added new `External` option to `Allocator` enum.
Added default constructors for `UnsafeList`, `UnsafeQueue`, and `UnsafeStack` using `Persistent` allocator.
Changed namespace in `AllocationManager` to `Misaki.HighPerformance.Unsafe.Buffer`.
Changed `MemoryLeakException` to use `MemoryLeakExceptionInfo` for better debugging.
Changed constructor behavior in `UnsafeArray` to clarify memory management responsibilities.
Changed `MemoryUtilities` to include null checks in `Free` and `AlignedFree` methods.
Removed unused using directive in `CollectionBenchmark.cs`.
Removed initialization of `AllocationManager` in `Program.cs`.

Misaki.HighPerformance.Unsafe/Collections/UnsafeStack.cs

@@ -23,6 +23,10 @@ public unsafe struct UnsafeStack<T> : IUnsafeCollection<T>
         return GetEnumerator();
     }
 
+    public UnsafeStack() : this(1, Allocator.Persistent)
+    {
+    }
+
     public UnsafeStack(int initialSize, Allocator allocator, AllocationOption allocationOption = AllocationOption.None)
     {
         _array = new UnsafeArray<T>(initialSize, allocator, allocationOption);