Add warning

cacheflow/worker/cache_engine.py

@@ -19,6 +19,9 @@ class CacheEngine:
         num_cpu_blocks: int,
         dtype: torch.dtype,
     ) -> None:
+        if head_size % 16 != 0:
+            raise ValueError(f'head_size ({head_size}) must be a multiple of 16.')
+
         self.worker_id = worker_id
         self.gpu_id = gpu_id
         self.num_layers = num_layers