Description of feature: I would like mod_register_limits to save its state to storage.
Motivation: the in-RAM throttling system is effective for per-connection throttling, but mod_register_limits reuses it for doing a longer-term. A "sensible value" as mentioned in the docs (https://prosody.im/doc/public_servers) is probably something like 24h-72h. It's fairly likely that a server will be restarted within that window. Currently, that means losing all the throttles that have been built up.