CLN: changed .format to f string in construction.py, dtypes/base.py, and dtypes/cast.py
- [X] ref [#29547](https://github.com/pandas-dev/pandas/issues/29547)
- [X] tests added / passed
- [X] passes `black pandas`
- [X] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

thanks @katieyounglove 