future annotations
- [x] closes #40533 
- [ ] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing.html#code-standards) for how to run them
sure, can you merge master once more and ping on green (of course in draft status) thanks @MarcoGorelli  @jreback @MarcoGorelli `from __future__ import annotations` is a Python 3.7+ feature*. Can I please check whether `pandas` no longer supports Python 3.6 and earlier versions of Python?

<sup>* See here: https://docs.python.org/3/whatsnew/3.7.html#pep-563-postponed-evaluation-of-annotations</sup> @rs2 that's right, Python3.6 is no longer supported