replace streaming.CollectStream with aggregatingStream

Created by: camdencheek

This replaces the weird callback method I made to collect a stream with a more idiomatic stream type that collects events as they come through. I find this easier to understand than the callback method, and it better matches what we do elsewhere with custom stream types.

I've wanted this type elsewhere to clean up some things, so I figured I'd convert the places we were using CollectStream first.