TYP: Annotations in pandas/core/{accessor, sorting}.py
- [ ] closes #xxxx
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

pending word from @simonjayhawkins on whetheer we bother annotating `-> None` for `__init__`, LGTM > pending word from @simonjayhawkins on whetheer we bother annotating `-> None` for `__init__`, LGTM

it's an undocumented convention that we're not annotating the return type of `__init__` Thanks @MomIsBestFriend 