Support update from ObjectNode

[emolter]

Closes #723

This PR allows model.update(d) to accept ObjectNode as d. See the added unit test for a realistic example of when this is helpful.

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]

https://github.com/spacetelescope/RegressionTests/actions/runs/25173273526

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.35%. Comparing base (e38b4eb) to head (d79fe3a).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #724   +/-   ##
=======================================
  Coverage   90.35%   90.35%           
=======================================
  Files          99       99           
  Lines        4582     4583    +1     
=======================================
+ Hits         4140     4141    +1     
  Misses        442      442           

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[melanieclarke]

Thanks for the fix!