Backdate ACA rating area premiums to 2018

[daphnehanse11]

fixes #7846

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.95%. Comparing base (f9a4a0f) to head (8cf3f46).
⚠️ Report is 415 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##              main    #7849       +/-   ##
============================================
- Coverage   100.00%   70.95%   -29.05%     
============================================
  Files            7     4103     +4096     
  Lines          215    59316    +59101     
  Branches         6      290      +284     
============================================
+ Hits           215    42087    +41872     
- Misses           0    17229    +17229     

Flag	Coverage Δ
unittests	70.95% <ø> (-29.05%)	⬇️

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[MaxGhenis]

I pushed a follow-up here.

What changed:

• added regression coverage around the ACA premium backfill so the new historical rating-area premium data is exercised by tests instead of landing as data-only changes

[MaxGhenis]

Reviewed the ACA premium regression coverage follow-up.