Typing: More precise NaT stub
- marked arguments in dunder methods positional only
  (important for subclassing and protocols)
- added `Period`, `np.datetime64` and `np.timedelta64` as compatible for `__add__` and `__sub__`
- added `np.datetime64` and `np.timedelta64`  as compatible with `__floordiv__` and `__truediv__`
- reworked comparisons:
  - removed protocol and use plain definition
  - changed return type from `bool` to `Literal[False]`
  - added `Self` to comparable types, so that `pd.NaT > pd.NaT` is considered valid


- [x] closes #60003 (Replace xxxx with the GitHub issue number)
- [ ] [Tests added and passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#writing-tests) if fixing a bug or adding a new feature
- [x] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
- [x] Added [type annotations](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#type-hints) to new arguments/methods/functions.
- [ ] Added an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature.



Thanks @randolf-scholz 