By: Michael Lynch <git@mtlynch.io>
Restore async video transcoding Stack slice-3 on top of slice-2.5 and reintroduce the durable background video transcode queue that slice-2.5 removed for a smaller diff.
| Time to Start | Worker time | Duration | Time to finish | |
| Config | 1s | 6s | 6s | 8s |
| Eval | 7s | 2m50s | 2m50s | 2m57s |
| Build | 3m22s | 3m54s | 1m50s | 5m13s |
| Suite | 1s | 6m51s | 5m11s | 5m13s |