WIP: Timestamp/DTA match stdlib tzawareness-compat behavior
- [x] closes #28507
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

I'm not super-happy with the implementation adding `op` kwarg to check_compatible_with and assert_tzawareness_compat, looking for something cleaner.
Mothballing to clear the queue