chore(docs): publish from RTD

[jeertmans]

ReadTheDocs offers two important features that GitHub pages do not:

1. builds versioning;
2. and build docs for PR (preview).

This is enough to motivate the migration to RTD.

I will keep a dummy GitHub pages site that redirects to RTD.

[github-actions]

Python benchmark results:

Legend:
  Outliers: 1 Standard Deviation from Mean; 1.5 IQR (InterQuartile Range) from 1st Quartile and 3rd Quartile.
  OPS: Operations Per Second, computed as 1 / Mean

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (014fb25) 86.53% compared to head (6ef0b06) 86.53%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #31   +/-   ##
=======================================
  Coverage   86.53%   86.53%           
=======================================
  Files          12       12           
  Lines         312      312           
=======================================
  Hits          270      270           
  Misses         42       42           

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