Add regression test for wfss_contam step for NIRISS

[emolter]

This PR adds a regression test for the wfss_contam step for NIRISS.

The test is analogous to the one that already exists for NIRCam. It runs the step with all the default options, except that all the intermediate files are saved. The segmentation map has been altered to contain only 15 sources instead of ~4000 to reduce runtime.

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)
    • 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

[emolter]

https://github.com/spacetelescope/RegressionTests/actions/runs/17687076003

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.41%. Comparing base (94c0254) to head (23f7b0d).
⚠️ Report is 8 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9830      +/-   ##
==========================================
+ Coverage   83.38%   83.41%   +0.03%     
==========================================
  Files         366      366              
  Lines       37770    37784      +14     
==========================================
+ Hits        31493    31518      +25     
+ Misses       6277     6266      -11     

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[emolter]

intermittent issues on Friday with crashing processes were thankfully unrelated (also present for one of the nightly runs) and tests are now passing on a rerun of the link above.

[melanieclarke]

Looks good - thanks for the additional coverage!