[SDK] Indefinitely retry events on network-related problems

As in the title, make processing events only increase their retry time if the problems are application-related, e.g. token error or "other" exceptions, no `M_LIMIT_EXCEEDED` and connection problems.

This'll make message-sending reliable through dodgy connections, and only then gives up if the server sends 500 errors and the like, which aren't programmatically sure to self-resolve in time anyway.