Replace `#` comments with modern docstrings when possible

In string.Formatter.{parse,get_field}, we use simple # comments to document methods. While it's picked up by pydoc (through inspect.getcomments()), it's not picked up by IDEs. I suggest we cleanup those occurrences to improve code readability as well. I stumbled upon it by chance so there might be other places that need such cleanup.

[!IMPORTANT]
Only comments that are above a def of a public function should be considered. Comments inside the function body or method body should be considered separately as it could also mean that the public API is incompletely documented on purpose (see https://github.com/python/cpython/issues/134082#issuecomment-2887461014 and following).

• Report including private names: https://gist.github.com/picnixz/d4aa5ff5e82013966dc575f0709c4398#file-full-report-md
• Report for publicly-named API: https://gist.github.com/picnixz/d4aa5ff5e82013966dc575f0709c4398#file-report-md

Both reports parse private files as well as they can be re-exported to a public API. We still need to go through each occurrences to check if they are expected to be exposed or not (and thus the task is NOT an easy task for newcomers).

Linked PRs

• gh-134083
• gh-134096
• gh-134125

Commencez par les commentaires au-dessus de string.Formatter.parse et de get_field, puis examinez les rapports sur l’API publique et les rapports complets liés dans l’issue. Vérifiez chaque occurrence signalée par rapport à la règle concernant les commentaires au-dessus des fonctions publiques, notamment si les noms privés sont réexportés. Le travail est terminé lorsque les occurrences appropriées utilisent des docstrings modernes, tandis que les commentaires intentionnellement conservés restent inchangés ; les PR liées gh-134083, gh-134096 et gh-134125 couvrent déjà des travaux connexes.