1/n inter batch parallelism

[tchaton]

What does this PR do?

This PR introduce the first component from #8959

Parts #8867
Parts #8316

Does your PR introduce any breaking changes? If yes, please list them.

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[codecov]

Codecov Report

Merging #9020 (2f305b0) into master (0461107) will increase coverage by 0%.
The diff coverage is 97%.

@@          Coverage Diff           @@
##           master   #9020   +/-   ##
======================================
  Coverage      93%     93%           
======================================
  Files         175     175           
  Lines       14361   14454   +93     
======================================
+ Hits        13312   13402   +90     
- Misses       1049    1052    +3     

[ethanwharris]

LGTM, small comments

[awaelchli]

LGTM
but the added test time is concerning me