typing improvements on level and fill_value in Series.eq
- [x] item 6 and 7 in [issue#11](https://github.com/noatamir/pyladies-aug23-sprint/issues/11)
- [x] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
pyladies-aug23-sprint : @phofl @noatamir  Thanks @color455nm !