Improve FreeList/TLSF allocators: alignment, GC, decommit

- FreeList: enforce min 16B alignment, use GCHandle for SharedState lifetime, switch to AllocZeroed, and use MemoryUtility for oversized allocs
- Add FreeList.CollectLocal() to flush thread-local caches
- TLSF: add decommitted flag, support front splitting for alignment, add Collect() to decommit large free blocks, use Munmap for cleanup
- Add VirtualMemoryBlock for virtual memory management
- Add tests for CollectLocal (FreeList) and Collect (TLSF)
- Update default allocator config and minor .csproj cleanup

Misaki.HighPerformance.Test/UnitTest/Buffer/TestFreeList.cs

@@ -177,4 +177,33 @@ public unsafe class TestFreeList
         freeList.Dispose();
         freeList.Dispose(); // Should not throw
     }
+
+    [TestMethod]
+    public void CollectLocal()
+    {
+        const int threadCount = 8;
+        const int iterations = 1000;
+        using var freeList = new FreeList(8, 64 * 1024);
+
+        var threads = new Thread[threadCount];
+        for (var i = 0; i < threadCount; i++)
+        {
+            threads[i] = new Thread(() =>
+            {
+                for (var j = 0; j < iterations; j++)
+                {
+                    var ptr = freeList.Allocate(128, 8);
+                    Assert.IsNotNull(ptr);
+                    freeList.Free(ptr);
+                }
+
+                freeList.CollectLocal();
+            });
+        }
+
+        foreach (var t in threads)
+            t.Start();
+        foreach (var t in threads)
+            t.Join();
+    }
 }

Misaki.HighPerformance.Test/UnitTest/Buffer/TestTlsfAllocator.cs

@@ -73,4 +73,16 @@ public class TestTlsfAllocator
             allocator.Free(ptrs[i]);
         }
     }
+
+    [TestMethod]
+    public unsafe void TestCollect()
+    {
+        using var allocator = TLSF.Create(new TLSF.CreationOptions { alignment = 16, initialChunkSize = 4096 * 1024 });
+        
+        var ptr = allocator.Allocate(1024 * 1024, 16);
+        Assert.IsTrue(ptr != null);
+        allocator.Free(ptr);
+
+        allocator.Collect();
+    }
 }