ref(buffer): Move project prefetch into push

[jjbayer]

Spooler V1 has been removed, so we can act upon this follow-up.

[Dav1dde]

Overall an improvement one less implicit requirement, it will however increase the load on the project cache (I assume 2x) since now there are 2 fetch calls happening:

1. in the "fast path" when accessing rate limits
2. another fetch from the buffer

Should observe usage and if it is a problem we can think of a solution which only conditionally triggers a fetch.