The arroyo produce step is potentially slower than sentry metrics indexer's produce step -- merge?

[untitaker]

https://github.com/getsentry/sentry/blob/4bc1642dcbe314a4b326ce2ff72445cd59b518d2/src/sentry/sentry_metrics/consumers/indexer/multiprocess.py#L21

this thing doesn't poll any produce futures, yet has been working fine in prod for a while. meanwhile for the spans indexer we are struggling to make arroyo's own produce step perform.

(TBD on whether the SimplePRoduceStep is actually faster)