remove fits extension assumption for hooks

[braingram]

This PR updates hooks to inherit output_ext from the hooked class.

Closes #216

JWST regtests: https://github.com/spacetelescope/RegressionTests/actions/runs/12938827091
Roman regtets: TBD after unit issues settle

Tasks

• update or add relevant tests
• update relevant docstrings and / or docs/ page
• Does this PR change any API used downstream? (if not, label with no-changelog-entry-needed)
  • write news fragment(s) in changes/: echo "changed something" > changes/<PR#>.<changetype>.rst (see below for change types)
  • run regression tests with this branch installed ("git+https://github.com/<fork>/stpipe@<branch>")
    • jwst regression test
    • romancal regression test

news fragment change types...

• changes/<PR#>.feature.rst: new feature
• changes/<PR#>.bugfix.rst: fixes an issue
• changes/<PR#>.doc.rst: documentation change
• changes/<PR#>.removal.rst: deprecation or removal of public API
• changes/<PR#>.misc.rst: infrastructure or miscellaneous change

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.28%. Comparing base (1acb486) to head (c947ebd).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #217   +/-   ##
=======================================
  Coverage   95.27%   95.28%           
=======================================
  Files          37       37           
  Lines        3177     3178    +1     
=======================================
+ Hits         3027     3028    +1     
  Misses        150      150           

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