CLN: Unify number recognition tests for all parsers
- [x] closes #38926
- [x] tests added / passed
- [x] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing.html#code-standards) for how to run them

Minor regex improvements.
Is a fixture the right thing to do here? 

very nice @phofl 