feat: creating mogodb and postgres mock instance in checkpoint test (#561)

* fix: using mongomock for the checkpoint test

* Add postgres mock setting to the unit test

* Added utils file of postgres_mock_utils

* fixed the runtime loading error of deerflow server

src/graph/checkpoint.py

@@ -368,5 +368,4 @@ def chat_stream_message(thread_id: str, message: str, finish_reason: str) -> boo
             thread_id, message, finish_reason
         )
     else:
-        logging.warning("Checkpoint saver is disabled, message not processed")
         return False