JP-4355: Move photom step after extract_1d step for WFSS modes

[emolter]

Resolves JP-4355

This PR moves the photom step to occur after extract_1d for WFSS data.

Implications:

• PhotomStep now expects WFSSMultiSpecModel as input.
• Extract1dStep now goes through a different logical path for WFSS modes, and step output when run standalone will be in DN/s units.
• The output x1d files from calwebb_spec2 will remain identical within roughly numerical precision.
• The output cal files from calwebb_spec2 will be in different units, since this product will no longer be flux-calibrated.

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 90.90909% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.08%. Comparing base (61fcd2d) to head (8015fff).

Files with missing lines	Patch %	Lines
jwst/photom/photom.py	95.00%	3 Missing ⚠️
jwst/pipeline/calwebb_spec2.py	25.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10718      +/-   ##
==========================================
- Coverage   87.11%   87.08%   -0.03%     
==========================================
  Files         374      374              
  Lines       40320    40354      +34     
==========================================
+ Hits        35123    35143      +20     
- Misses       5197     5211      +14     

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[emolter]

initial regression test attempt https://github.com/spacetelescope/RegressionTests/actions/runs/29605834306