fix(freelist): ensure at least one block is created

Updated FreeList allocator to guarantee at least one block is created per chunk by using Math.Max(1u, ...), and capped the number of blocks at 256. This prevents blocksToCreate from being zero and improves allocator robustness.

Bumped assembly version to 1.6.3.

Misaki.HighPerformance.LowLevel/Buffer/FreeList.cs

@@ -385,7 +385,9 @@ public unsafe struct FreeList : IMemoryAllocator<FreeList, FreeList.CreationOpts
             }
 
             var blockSize = bucket->blockSize;
-            var blocksToCreate = Math.Min(_chunkSize / blockSize, 256);
+            var blocksToCreate = Math.Max(1u, _chunkSize / blockSize);
+            blocksToCreate = Math.Min(blocksToCreate, 256);
+
             if (blocksToCreate == 0)
             {
                 return false;