BUG: Assorted DTA/TDA/PI bugfixes
Fixes a problem with tz-aware DatetimeArray.round (ref #24038)
Fixes PI, PA, DTA failing to validate lengths when doing comparisons against length-1 instances (ref #23078)
Pins names to a handful of methods that currently don't have them (working on a separate branch that checks these systematically; these are the low-hanging fruit)

- [x] closes #23078
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry
