JP-3930: coron tests and minor fixes

[melanieclarke]

Partially resolves JP-3930

While adding some basic smoke tests for the coron steps for JP-3930, I noticed a couple minor bugs:

• AlignRefsStep returns None if no reference file is found
• KlipStep does not close the PSF model after opening it
• median_image_replace crashes for MIRI data if there are no bad pixels
• median_image_replace handles NaNs incorrectly if they're not flagged in the DQ plane

I fixed these here and filled out unit test coverage to 100%.

I also noticed that HlspStep is unused in any pipeline, has not been modified recently, and expects different inputs than the rest of the coron steps. I filed JP-4069 to ask if we should remove or update it.

I think no changelog entry is needed, since the bugs were not likely to have been encountered by users, but I can add one if desired.

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

[melanieclarke]

Regtests:
https://github.com/spacetelescope/RegressionTests/actions/runs/16502625487

All passing.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
⚠️ Please upload report for BASE (main@e5d37a1). Learn more about missing BASE report.
⚠️ Report is 230 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #9693   +/-   ##
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  Coverage        ?   82.49%           
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  Files           ?      366           
  Lines           ?    37129           
  Branches        ?        0           
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  Hits            ?    30629           
  Misses          ?     6500           
  Partials        ?        0           

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[stscirij]

Look great! 100% coverage too. As usual I learned a bunch by looking at this

[tapastro]

👍