Persist events that not yet have a handler

There's a risk that a event is emitted before its' handler has been registered. You might say that such code is bad design, but I'd like to be lazy ;) Also, given that code splitting is being more and more adopted, I think this scenario is very real.

Would it be possible to persist events that don't have a handler (yet)? Whenever `.on(...)` is run, mitt would then check the persisted events in order to find unprocessed ones, and then handle those events immediately.

I think the footprint for this change can be quite small, but I can't speak for performance. Maybe we can opt-in to the behaviour.

Lisez le point d’entrée actuel de l’émetteur TypeScript et ses tests existants afin de comprendre comment se comportent emit et .on(...) lorsqu’aucun handler n’est enregistré. Définissez le comportement de persistance opt-in, notamment les attentes en matière d’ordre, de replay et de performances ; le travail est considéré comme terminé lorsque les événements non gérés sont conservés et délivrés lorsqu’un handler est enregistré ultérieurement, sans modifier le comportement par défaut.

Rédigé par le modèle d'indexation à partir du texte de l'issue.