Event creation rate limiting happens very late in a worker environment

This issue has been migrated from [#16481](https://github.com/matrix-org/synapse/issues/16481).

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When event persistence happens in a separate worker process to event creation, we don't end up applying the ratelimit until the event reaches the event persister.

This means we end up doing *lots* of work (including calculating the push actions and inserting into `event_push_actions_staging`) for an event that gets thrown away.

There is code to attempt to apply the ratelimiter upfront (https://github.com/matrix-org/synapse/blob/v1.93.0/synapse/handlers/message.py#L1001-L1002), but it doesn't work in a worker environment because the count is never updated.