JP-3923: Localize test warnings (try 2), fix test data packaging, misc test clean-ups

[pllim]

Resolves JP-3923

xref #1397

close #9325

This PR localizes test warnings as much as possible. This is basically #9325 but without the blind RuntimeWarning ignores that raised concerns. In place of those ignores are now # FIXME comment for the future. Global test warning filters now remain untouched to avoid failing regtest that is peppered with warnings. The -W error in tox.ini theoretically should be enough to turn all unhandled warnings in regular CI using tox into exceptions. 🤞

Tasks

• If you have a specific reviewer in mind, tag them.
• add a build milestone, i.e. Build 12.0 (use the latest build if not sure)
• Does this PR change user-facing code / API? (if not, label with no-changelog-entry-needed)
  • write news fragment(s) in changes/: echo "changed something" > changes/<PR#>.<changetype>.rst (see changelog readme for instructions)
  • update or add relevant tests
  • update relevant docstrings and / or docs/ page
  • start a regression test and include a link to the running job (click here for instructions) https://github.com/spacetelescope/RegressionTests/actions/runs/14344612421 and https://github.com/spacetelescope/RegressionTests/actions/runs/14385535286
    • Do truth files need to be updated ("okified")?
      • after the reviewer has approved these changes, run okify_regtests to update the truth files
• if a JIRA ticket exists, make sure it is resolved properly

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 75.39%. Comparing base (1c93ca5) to head (d32c679).
Report is 673 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #9381   +/-   ##
=======================================
  Coverage   75.39%   75.39%           
=======================================
  Files         368      368           
  Lines       36842    36842           
=======================================
  Hits        27777    27777           
  Misses       9065     9065           

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[pllim]

With this PR, you will notice that there are no warnings in the CI test logs, but still warnings in RT (https://github.com/spacetelescope/RegressionTests/actions/runs/14344612421/job/40211860319). Both passed.

[pllim]

https://github.com/spacetelescope/RegressionTests/actions/runs/14366715093/attempts/1#summary-40281436373 passed except 1 known failure in devdeps

[melanieclarke]

I think this looks good now, except for the one CI change that I think we should move to a separate PR. Remind us if we don't come back around to properly cleaning up the warnings in the regression tests.

I'll leave this open for today in case anyone else wants to review.

[pllim]

Thanks for your patience!