TYP: stubs for tslibs
- [ ] closes #xxxx
- [ ] tests added / passed
- [ ] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing.html#code-standards) for how to run them
- [ ] whatsnew entry

in setup.cfg we have `ignore_missing_imports = True`. This is probably the next strictness flag we should consider changing.

we this PR have 393 errors, 162 of these are from pandas._libs

on master we have 407 errors (176 pandas._libs)

so a good start. Thanks @jbrockmendel 