Fix bug preventing NirspecQuadFlatModel instantiation from NirspecFlatModel

[emolter]

Closes #186

This PR fixes a bug where attempting to initialize a NirspecQuadFlatModel from a NirspecFlatModel would raise TypeError: dynamic_mask() missing 1 required positional argument: 'mnemonic_map'.

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 jwst regression tests with this branch installed ("git+https://github.com/<fork>/stdatamodels@<branch>")

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

[emolter]

regression tests started here https://github.com/spacetelescope/RegressionTests/actions/runs/13293800994

edit: failures are unrelated. They match the expected failures from merging the resample changes in jwst: https://github.com/spacetelescope/RegressionTests/actions/runs/13292323770

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.41%. Comparing base (4e83608) to head (455c881).
Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #401      +/-   ##
==========================================
+ Coverage   78.16%   78.41%   +0.24%     
==========================================
  Files         115      115              
  Lines        5144     5152       +8     
==========================================
+ Hits         4021     4040      +19     
+ Misses       1123     1112      -11     

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[braingram]

LGTM. Thanks!