Fix the error when using create_sql_agent

[reatang]

fix error: "pydantic.errors.PydanticUndefinedAnnotation: name 'BaseCache' is not defined"

error stack

    |     ret = await asyncio.create_task(coro, context=context)
    |           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |   File "/Users/reatang/www/demo-agent-service/src/my_agents/graph.py", line 78, in score_query
    |     sql_agent = create_sql_agent(llm=llm, db=db, prompt=prompt)
    |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |   File "/Users/reatang/www/demo-agent-service/.venv/lib/python3.12/site-packages/langchain_community/agent_toolkits/sql/base.py", line 141, in create_sql_agent
    |     toolkit = toolkit or SQLDatabaseToolkit(llm=llm, db=db)  # type: ignore[arg-type]
    |                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |   File "/Users/reatang/www/demo-agent-service/.venv/lib/python3.12/site-packages/pydantic/main.py", line 214, in __init__
    |     validated_self = self.__pydantic_validator__.validate_python(data, self_instance=self)
    |                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |   File "/Users/reatang/www/demo-agent-service/.venv/lib/python3.12/site-packages/pydantic/_internal/_mock_val_ser.py", line 100, in __getattr__
    |     raise PydanticUserError(self._error_message, code=self._code)
    | pydantic.errors.PydanticUserError: `SQLDatabaseToolkit` is not fully defined; you should define `BaseCache`, then call `SQLDatabaseToolkit.model_rebuild()`.
    | 
    | For further information visit https://errors.pydantic.dev/2.10/u/class-not-fully-defined