* [Refactor] Refactor the rest data transforms and fix some docstring.
* Use `mmengine` instead of `mmcv`
* Refactor KFold dataset tools
* Fix docstring according to comments
* Support to use `indices` to specify which samples to evaluate.
* Add KFoldDataset wrapper
* Rename 'K' to 'num_splits' accroding to sklearn
* Add `kfold-cross-valid.py`
* Add unit tests
* Add help doc and docstring