* Replace markdownlint with mdformat to avoid installing ruby

* fix circleci

* try to fix lint

* upgrade yapf version

* use another way to bypass yapf

* update docstring

* Add circleci

* fix typo

* lower required coverage

* support initialzing distributed environemtn without GPUs

* fix unit tests

* add approval for running gpu tests

* add approval for running gpu tests

* fix unit tests

* fix unit tests