* refactor: remove usage of global variables in abbrevs.py
* chore: add flake8-mutable to prevent mutable defaults
* fix: abbrevs expand test
* refactor: add xonsh session singleton
* refactor: fix circular errors when using xonshSession as singleton
* refactor: remove black magicked builtin attributes
* style: black format tests as well
* refactor: update tests to use xonsh-session singleton
* refactor: update abbrevs to not use builtins
* test: remove DummyCommandsCache and patch orig class
* fix: failing test_command_completers
* test: use monkeypatch to update xession fixture
* fix: failing test_pipelines
* fix: failing test_main
* chore: run test suit as single invocation
* test: fix tests/test_xonsh.xsh
* refactor: remove builtins from docs/conf.py
* fix: mypy error in jobs
* fix: test error from test_main
* test: close xession error in test_command_completers
* chore: use pytest-cov for reporting coverage
this will include subprocess calls, and will increase coverage
* style:
