BUG: algos.diff with datetimelike and NaT
- [ ] closes #xxxx
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

where is the bug? > where is the bug?

`algos.diff`.  the tests this adds fails in master