GitLab

* [Feature] Choose storage backend by the prefix of filepath

* refactor FileClient and add unittest

* support loading from different backends

* polish docstring

* fix unittet

* rename attribute str_like_obj to is_str_like_obj

* add infer_client method

* add check_exist method

* rename var client to file_client

* polish docstring

* add join_paths method

* remove join_paths and add _format_path

* enhance unittest

* refactor unittest

* singleton pattern

* fix test_clientio.py

* deprecate CephBackend

* enhance docstring

* refactor unittest for petrel

* refactor unittest for disk backend

* update io.md

* add concat_paths method

* improve docstring

* improve docstring

* add isdir and copyfile for file backend

* delete copyfile and add get_local_path

* remove isdir method of petrel

* fix typo

* add comment and polish docstring

* polish docstring

* rename _path_mapping to _map_path

* polish docstring and fix typo

* refactor get_local_path

* add list_dir_or_file for FileClient

* add list_dir_or_file for PetrelBackend

* fix windows ci

* Add return docstring

* polish docstring

* fix typo

* fix typo

* deprecate the conversion from Path to str

* add docs for loading checkpoints with FileClient

* refactor map_path

* add _ensure_methods to ensure methods have been implemented

* fix list_dir_or_file

* rename _ensure_method_implemented to has_method