[Fix] Fix `BaseDataPreprocessor.cast_data` cound not handle string data (#602)

* [Fix] Fix  cound not handle string data

* Minor refine

* Refine type hint

Refine type hint

* fix as comment

* Minor refine

* Update mmengine/model/base_model/data_preprocessor.py

Co-authored-by: Zaida Zhou <58739961+zhouzaida@users.noreply.github.com>