* add docs for custom dataset wrapper

* Update basedataset.md

* refactor docs of basedataset

* fix ci

* fix comments

* fix comments

* fix comments

* fix comments

* fix comments

* set default value of ann_file to ''

* fix comments

* Fix BaseDataset docs

* Fix basedataset doc

* 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>

* add docs for BaseDataset

* update docs

* update docs

* update basedataset.md

* resolve all comments

* update

* update

* refine base dataset doc

* resolve all comments

* update

* update

* update

* update

* update

* update

* update

Co-authored-by: MeowZheng <meowzheng@outlook.com>