Use the standard lib tomllib, or default to tomli if not available

[mwouts]

Closes #1195

[github-actions]

Thank you for making this pull request.

Did you know? You can try it on Binder: or .

Also, the version of Jupytext developed in this PR can be installed with pip:

pip install git+https://github.com/mwouts/jupytext.git@use_tomllib_or_tomli

(this requires nodejs, see more at Developing Jupytext)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.73%. Comparing base (642c709) to head (e9c56ab).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1200   +/-   ##
=======================================
  Coverage   97.73%   97.73%           
=======================================
  Files          29       29           
  Lines        4463     4464    +1     
=======================================
+ Hits         4362     4363    +1     
  Misses        101      101           

Flag	Coverage Δ
external	75.17% <75.00%> (+0.14%)	⬆️
functional	88.51% <75.00%> (+0.02%)	⬆️
integration	77.28% <100.00%> (+<0.01%)	⬆️
unit	66.56% <87.50%> (+<0.01%)	⬆️

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