* basedataset first commit

* add base dataset

* add dataset

* add basedataset

* Fix test dataset

* Fix mypy and test

* Fix mypy and test

* remove unused code

* Update mmengine/dataset/base_dataset.py

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

* Update mmengine/dataset/base_dataset.py

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

* add more corner cases in unittest

* fix lint

* Fix as comment

* Fix lint

* update unitest

* Type hint Dick to dict

* rename max_refetch

* Fix as comment

* Fix typo

* Fix as comment

* BaseDataset is no more an abstrac Class, change UT and docs

* Fix as comment

* Fix as comment and refactor type error

* Add comment for full init

* Fix as comment and modify dataset_wrapper

* Fix as comment and modify dataset_wrapper

* Fix as comment

* Fix as comment

* Fix as comment

* Fix as comment

* Fix as comment

* Fix as comment

* Fix as comment

Co-authored-by: Zaida Zhou <58739961+zhouzaida@users.noreply.github.com>
Co-authored-by: Tao Gong <gongtao950513@gmail.com>

* move fileio directory from utils

* remove CephBackend from fileio and clear some deprecated docstring

* fix format

* fix a spellling error

* tmp commit

* add unittest for basedataset

* fix lint

* resolve all comments

* update

* update

* update

* update

* update

* update

* update

* resolve comments

* resolve comments

* update

* resolve comments

* resolve comments