BUG/Compat: dt64/td64 cummin, cummax on np 1.18
- [x] closes #29058
- [x] closes #15553
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

This also fixes+tests Series cummin/cummax with dt64tz, will have to look to see if there are any GH issues for that.

Following this and #29872 I think we should refactor a bunch of this out into core.nanops.
Fixes at least one of the cases in #15553, will see if the others are already fixed+tested