un-WIP scRNA Core pipeline record loader files

[harrietc52]

Closes #4344

Dependencies

sanger/limber#1939

Changes proposed in this pull request

• un-WIP scRNA Core pipeline record loader files

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.59%. Comparing base (fa75ca3) to head (fa6f4d5).
Report is 48 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #4352      +/-   ##
===========================================
- Coverage    87.62%   87.59%   -0.04%     
===========================================
  Files         1383     1383              
  Lines        29881    29881              
===========================================
- Hits         26183    26174       -9     
- Misses        3698     3707       +9     

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[andrewsparkes]

We'll want to deploy this change to training first along with the corresponding Limber WIP changes, and run the scRNA integration suite test against it. So maybe not merge into develop immediately? Can discuss with other scRNA devs.