Instead of needing to individually disable throttling on a per-plugin
basis, this fixture takes care of all notifiers in `NOTIFY_MODULE_MAP`
automatically. With `autouse=True`, there is no need to activate it
manually.
While the namespace is physically made of modules, it has been amended
to be the namespace home for the corresponding notifier classes as well.
This turned out to confuse both humans and machines on various ends.
While it has apparently worked for a while, it croaks on Python 3.11
now, and is not considered to have been a good idea in general.
