Run doctest in CI and fix errors in the documentation examples

[LegrandNico]

This PR will contribute to #1191 by:

• [ ] Creating a new action that runs doctest in CI (not working for now).
• [ ] Fix the errors already present in the documentation (55 / 145 error remains).

The remaining errors are less trivial than formatting issues and will probably require more careful editing.

I also have trouble fixing errors where the structure of a graph is returned, pasting the actual output is not enough here, this is probably due to whitespace formatting (see the NORMALIZE_WHITESPACE option from doctest?).

[codecov[bot]]

Codecov Report

Merging #1193 (dd22ff2) into main (69c1044) will not change coverage. The diff coverage is n/a.

Additional details and impacted files

@@           Coverage Diff            @@
##             main    #1193    +/-   ##
========================================
  Coverage   79.13%   79.13%            
========================================
  Files         173      173            
  Lines       48492    48492            
  Branches    10966    10309   -657     
========================================
  Hits        38374    38374            
  Misses       7625     7625            
  Partials     2493     2493            

Impacted Files	Coverage Δ
aesara/gradient.py	77.16% <ø> (ø)
aesara/graph/basic.py	89.00% <ø> (ø)
aesara/tensor/rewriting/math.py	87.28% <ø> (ø)

[rlouf]

Is there anything outstanding here @LegrandNico, besides the conflicts?

[LegrandNico]

I can work on it a bit later today. I had difficulties creating a new action and I was not sure if this should be a part of the test.yml or a new file.

[rlouf]

I can work on it a bit later today. I had difficulties creating a new action and I was not sure if this should be a part of the test.yml or a new file.

Great! I think a doctests.yml file is fine for now, let's focus on getting the doc tests running in CI in this PR and we can always move them later. Once this is running it will be easier to keep track of the remaining errors.