populate phase should use dynamic rate limiter

Currently it uses the fixed rate limiter. Best option would be to let it go as fast as possible. Maybe use a target of 50K to let it step up fairly quickly then let it dial in itself.

Locate the populate phase and its current fixed rate limiter, then trace how limiter targets are configured and updated. Compare the available dynamic-limiter behavior with the suggested 50K starting target; done means populate uses the dynamic limiter and its rate converges as intended, with relevant tests updated or added.

Written by the indexing model from the issue text.