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.

Leggi Documentation/Style Guide/Code Examples e la documentazione di doctest, in particolare gli esempi interattivi e le indicazioni sulle direttive. Esamina il controllo Docs/Doctest CI e le discussioni citate per stabilire la policy attuale, quindi aggiungi un riepilogo conciso nella sezione esistente o in una nuova sezione immediatamente successiva. Il lavoro è completato quando la guida spiega il comportamento previsto di doctest e le direttive rilevanti per gli esempi interattivi.