[ENHANCEMENT] Doctesting

[oerc0122]

Is your feature request related to a problem? Please describe.
Documentation has fallen out of date for some functions or these functions produce unexpected results not described. doctest provides a mechanism for ensuring the documentation does not fall out of date and integrates with pytest

Describe the solution you'd like
Ensure documentation is valid, up-to-date and correct throughout and integration of doctesting into the CI

Describe alternatives you've considered
N/A

Additional context
Currently pytest --doctest-modules fails to run due to the following

Run results

ERROR Doc/conf_api.py - AttributeError: 'str' object has no attribute '__name__'. Did you mean: '__ne__'?
ERROR Doc/conf_help.py - AttributeError: 'str' object has no attribute '__name__'. Did you mean: '__ne__'?
ERROR Src/MDANSE/Framework/Formats/SVGFormat.py
ERROR Src/MDANSE/IO/FortranFormat.py - ValueError: line 11 of the docstring for MDANSE.IO.FortranFormat lacks blank after >>>: "    >>>s = '   59999'"