Mark test_computationerror_ipython as flaky

[khaeru]

This test fails sporadically with CellTimeoutError.

Add pytest-rerunfailures to [tests] optional dependencies.

Also:

• Replace a Sphinx build step in the "pytest" CI workflow with the ReadTheDocs automated PR build & associated check.
• Force a daily refresh of the cached environment for mypy via pre-commit.

PR checklist

• Checks all ✅
• Update documentation N/A; test/CI changes only
• Update doc/whatsnew.rst N/A

[codecov-commenter]

Codecov Report

Merging #107 (8f8fd95) into main (9398a42) will not change coverage.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #107   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           48        48           
  Lines         4040      4043    +3     
=========================================
+ Hits          4040      4043    +3     

Files	Coverage Δ
genno/tests/core/test_exceptions.py	100.00% <100.00%> (ø)