Add new property expected_output_dataframe_type for gokart.TaskOnKart which allows the users to provide the Pandera schema. If expected_output_dataframe_type is provided, when loading (load) and storing (dump) the cached dataframe, it will automatically check if the dataframe meet the schema defined in expected_output_dataframe_type. See test/test_task_on_kart.py for example usage.

[must] fix error from mypy