Add discussion of doctesting interactive code examples.

There have been various discussions about doctesting interactive code examples in the python docs. The consensus has been that it is desirable that they pass. Indeed, CI currently has a (pass-not-required) Tests / Docs / Doctest. (But it seems to be setup to be excessively lenient, passing many errors that are normally caught. Intended? Bug?) There has been additional discussion about use of particular features, such as doctest directives. An example from the doc:

The [ELLIPSIS](https://docs.python.org/3/library/doctest.html#doctest.ELLIPSIS) directive
gives a nice approach for the last example:
>>> C()  # doctest: +ELLIPSIS
<C object at 0x...>

Other people may remember such discussions better. In any case, a summary of current policy should be added either in
Documentation / Style Guide /Code Examples or in a new "Interactive Code Examples and Doctest" section immediately after.

Lisez Documentation/Style Guide/Code Examples et la documentation de doctest, en particulier les exemples interactifs et les indications concernant les directives. Examinez la vérification Docs/Doctest CI et les discussions référencées afin d’établir la politique actuelle, puis ajoutez un résumé concis dans la section existante ou dans une nouvelle section immédiatement après. La tâche est terminée lorsque le guide explique le comportement attendu de doctest et les directives pertinentes pour les exemples interactifs.