Add type hinting to public-facing API  in pandas/core/generic.py #26792
- [x] Part of #26792
- [x] tests passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
you need to run `isort pandas/core/generic.py` closing as stale, some of this has been done, welcome for PRs to continue