fix import error

Author: yexin

examples/update.py

@@ -14,7 +14,8 @@
 from loguru import logger
 from safetensors import safe_open
 
-from checkpoint_engine.ps import ParameterServer, request_inference_to_update
+from checkpoint_engine.ps import ParameterServer
+from checkpoint_engine.api import request_inference_to_update
 
 
 @contextmanager