JP-3805: Change prior-group flagging to DO_NOT_USE instead of SATURATION

[drlaw1558]

This PR addresses the issue raised by JP-3805 wherein the flagging of saturation in group-averaged data by estimating the counts in each frame can bias the finding and flagging of snowballs downstream. This does so by changing the flagging of such 'pre-saturation' to use DO_NOT_USE instead of SATURATED.

Tasks

• update or add relevant tests
• update relevant docstrings and / or docs/ page
• Does this PR change any API used downstream? (if not, label with no-changelog-entry-needed)
  • write news fragment(s) in changes/: echo "changed something" > changes/<PR#>.<changetype>.rst (see below for change types)
  • run regression tests with this branch installed ("git+https://github.com/<fork>/stcal@<branch>")
    • jwst regression test
    • romancal regression test

news fragment change types...

• changes/<PR#>.apichange.rst: change to public API
• changes/<PR#>.bugfix.rst: fixes an issue
• changes/<PR#>.general.rst: infrastructure or miscellaneous change

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 29.57%. Comparing base (8f0186b) to head (35726e9).
Report is 11 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #321      +/-   ##
==========================================
+ Coverage   28.69%   29.57%   +0.88%     
==========================================
  Files          31       36       +5     
  Lines        7821     7949     +128     
==========================================
+ Hits         2244     2351     +107     
- Misses       5577     5598      +21     

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[melanieclarke]

@tapastro - do we want this in build 11.2?

[tapastro]

After some work by @schlafly to relax romancal tests which allow this PR to pass testing, and jwst RT passing: https://github.com/spacetelescope/RegressionTests/actions/runs/12432943298

We can merge this. I will file a JP ticket to track further investigation of the snowball code, which will hopefully lead to a PR with changes to snowball code and a reversion of this update.