JP-4196: Update NIS_WFSS exptype to expect per-wavelength units in photom ref file

[emolter]

Resolves JP-4196

Closes #10058

This PR updates the photom and wfss_contam steps to expect per-wavelength units in NIRISS WFSS photometric reference file data, similar to what is already done for NIRCam.

Please note that this requires a coordinated reference file delivery.

https://github.com/spacetelescope/RegressionTests/actions/runs/21487386050
Regression tests are expected to have very large differences for all NIRISS WFSS data downstream of the photom step, and for tests where wfss_contam is turned on. I'd expect the differences to be much smaller (say, a few percent or less) when pointed to the new ref file.
These tests are useful to show that only the products we'd expect to change have changed.

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)
    • if your change breaks step-level or public API (as defined in the docs), 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

❌ Patch coverage is 83.33333% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.66%. Comparing base (bbf1e5f) to head (3d22354).
⚠️ Report is 75 commits behind head on main.

Files with missing lines	Patch %	Lines
jwst/wfss_contam/sens1d.py	71.42%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10199      +/-   ##
==========================================
- Coverage   85.98%   84.66%   -1.33%     
==========================================
  Files         368      366       -2     
  Lines       38457    38463       +6     
==========================================
- Hits        33066    32563     -503     
- Misses       5391     5900     +509     

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[emolter]

the mock photom ref file sensitivities are all set to unity for this test, so it stands to reason that the value we are checking would change substantially.

[emolter]

@KevinVolkSTScI is still doing some analysis of the new photom output values with this PR, but they're within 1% of the old values so if there's any code issue, it's almost certainly due to some pre-existing issue, not the code changes here. Therefore I'm marking this ready for review now.