feat(memory): improve oversized alloc handling & cleanup

Enhanced FreeList to handle oversized allocations by bypassing chunk management and allocating directly from the OS, with proper header assignment and immediate release on free. Updated IUnsafeCollection<T> documentation, removed unnecessary array clearing in Clear() methods, refined UnsafeSlotMap initialization logic, and removed redundant default element addition. Bumped assembly version to 1.5.1.

Misaki.HighPerformance.LowLevel/Collections/Contracts/IUnsafeCollection.cs

@@ -28,7 +28,7 @@ public interface IUnsafeCollection<T> : IUnsafeCollection, IEnumerable<T>
     where T : unmanaged
 {
     /// <summary>
-    /// Gets the number of elements in a collection. The value is read-only.
+    /// Gets the number of elements in a collection.
     /// </summary>
     int Count
     {

Misaki.HighPerformance.LowLevel/Collections/UnsafeList.cs

@@ -467,7 +467,6 @@ public unsafe struct UnsafeList<T> : IUnsafeCollection<T>
 
     public void Clear()
     {
-        _array.Clear();
         _count = 0;
     }
 

Misaki.HighPerformance.LowLevel/Collections/UnsafeQueue.cs

@@ -193,7 +193,6 @@ public unsafe struct UnsafeQueue<T> : IUnsafeCollection<T>
 
     public void Clear()
     {
-        _array.Clear();
         _count = 0;
         _offset = 0;
     }

Misaki.HighPerformance.LowLevel/Collections/UnsafeSlotMap.cs

@@ -132,8 +132,8 @@ public unsafe struct UnsafeSlotMap<T> : IUnsafeCollection<T>
         if (!allocationOption.HasFlag(AllocationOption.Clear))
         {
             _generations.AsSpan().Clear();
+            _validBits.ClearAll();
         }
-        _validBits.ClearAll();
 
         _count = 0;
         _capacity = capacity;
@@ -324,8 +324,6 @@ public unsafe struct UnsafeSlotMap<T> : IUnsafeCollection<T>
         _validBits.ClearAll();
 
         _count = 0;
-
-        Add(default, out _);
     }
 
     public readonly void* GetUnsafePtr()

Misaki.HighPerformance.LowLevel/Collections/UnsafeSparseSet.cs

@@ -396,8 +396,6 @@ public unsafe struct UnsafeSparseSet<T> : IUnsafeCollection<T>
 
         _count = 0;
         _nextId = 0;
-
-        Add(default, out _);
     }
 
     /// <inheritdoc/>

Misaki.HighPerformance.LowLevel/Collections/UnsafeStack.cs

@@ -221,7 +221,6 @@ public unsafe struct UnsafeStack<T> : IUnsafeCollection<T>
 
     public void Clear()
     {
-        _array.Clear();
         _count = 0;
     }