DOC: frame.py doctest fixing
- [ ] fixes part of #22459 for the `DataFrame` methods
- [ ] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

The PR provides some onging fixes for doctetsts #22459 focusing on the methods of `frame.py`. At the same time, the involved docstrings were corrected using the validation script. I removed the methods I effectively adapted from the `ci/code_checks.sh`