Implement method to populate meta.statistics attribute for datamodels.

[mairanteodoro]

Resolves RCAL-999

This PR implements a new romancal.lib.statistics.populate_statistics() helper and wires it into RomanStep.finalize_result() so that any Roman step that produces an ImageModel or MosaicModel output will have meta.statistics populated automatically.

Regression tests

• https://github.com/spacetelescope/RegressionTests/actions/runs/23815735809 (03/31/26)
  • All failing tests are due to the new meta.statistics attribute being added, which will be fixed once the truth files have been "okified."

Tasks

• request a review from someone specific, to avoid making the maintainers review every PR
• add a build milestone, i.e. 24Q4_B15 (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)
    • if your change breaks existing functionality, also add a changes/<PR#>.breaking.rst news fragment
  • 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

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.63%. Comparing base (683c428) to head (cfd7106).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2248      +/-   ##
==========================================
+ Coverage   80.58%   80.63%   +0.05%     
==========================================
  Files         155      156       +1     
  Lines        9341     9368      +27     
==========================================
+ Hits         7527     7554      +27     
  Misses       1814     1814              

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[ddavis-stsci]

LGTM

[braingram]

Thanks for putting this together. Now that statistics is populated would you remove the "junk" value setting in resample:

romancal/romancal/resample/resample_step.py

Lines 180 to 183 in 2aaaad7

	# TODO statistics are unknown
	model.meta.statistics.image_median = np.nan
	model.meta.statistics.image_rms = np.nan
	model.meta.statistics.good_pixel_fraction = np.nan

[braingram]

Thanks! Code updates look good to me. Let's wait for @schlafly to weight in on the differences and to clarify what should be done for L3 files. Specifically, should they have zodiacal_light populated?

[schlafly]

This looks like a good implementation to me; I would not have thought of doing it through finalize_result, but it's nice that that means that all intermediate products get flags too.

I have a suggestion below for only computing the medians and rmses from the good pixels, though I don't expect that to make a meaningful difference in practice.

Let's not populate zodiacal_light for L3 files; it's not in the schema and it doesn't make a lot of sense.

[schlafly]

It looks like my suggestion fails because err does not exist. It's required, though, so I'm a bit confused; presumably some test code hadn't needed it before and now is failing?

[mairanteodoro]

Yes, I'm updating the code and unit tests to account for that.