ENH: use stdlib tomllib when available (Python 3.11)

[neutrinoceros]

Bug report

Bug summary

tomli is currently a hard dependency third party, but it's been integrated to the standard library as tomllib and will be available in Python 3.11
Because it's the same underlying implementation, this means we should be able to use tomli as a "backport" of tomllib in Python 3.10 and older as

import sys

if sys.version_info >= (3, 11):
    import tomllib
else:
    import tomli as tomllib

However I'd rather not implement this just now, because Python 3.11 isn't testable yet: we depend on numpy for this. Here's the upstream PR to keep track of numpy/numpy#21308

[neutrinoceros]

update: numpy just started testing with Python 3.11, next up is kiwi solver (build time requirement, required by setuptools):
nucleic/kiwi#141