* feat: broadcast_object_list & scatter_object_list

* chore: update ut conf

* get_backend & is_available

* docs: update requirements

* fix: resolve conflicts
Co-authored-by: NLiYuRio <liyuruijx@163.com>

* delete legacy dygraph code in python/paddle/distributed

* refine

* isort all files

* revert conflicting files

* revert conflicting files

* revert conflicting files

* refactor: move wait

* refactor: move barrier

* fix: fix incorrect import

* refactor: move all_gather

* feat: static check

* [CodeStyle][py2][U004] unecessary explicit `object` inheritance in class definition

* fix an increment

* update config

* re-blacken python code

* temporarily disable date and diff_py_file

* skip a format

* refactor mp.

* update setup.py.

* update mp_layers.py for compatibility.

* add documents for mp_layers.py

* update init.py

* update collective.py.

* update.

* update mp_ops.py

* update.

* update code style.

* update code style.