Support Python 3.11

[hugovk]

In beta next week, full release in October: https://peps.python.org/pep-0664/

Plus update some config.

[codecov]

Codecov Report

Merging #77 (4ce8cbd) into main (a584dcb) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main      #77   +/-   ##
=======================================
  Coverage   95.76%   95.76%           
=======================================
  Files           8        8           
  Lines         354      354           
=======================================
  Hits          339      339           
  Misses         15       15           

Flag	Coverage Δ
GHA_Ubuntu	?
GHA_Windows	?
GHA_macOS	?
macos-latest	95.76% <ø> (?)
ubuntu-latest	95.76% <ø> (?)
windows-latest	95.76% <ø> (?)

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