add 3.15 testing

[braingram]

blocked by pyarrow: https://pypi.org/project/pyarrow/

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 changelog readme for instructions)
  • if your change breaks existing functionality, also add a changes/<PR#>.breaking.rst news fragment
• run regression tests with this branch installed ("git+https://github.com/<fork>/stcal@<branch>")
  • jwst regression test
  • romancal regression test

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.92%. Comparing base (6583136) to head (0d89ddf).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #579   +/-   ##
=======================================
  Coverage   91.92%   91.92%           
=======================================
  Files          63       63           
  Lines        8925     8925           
=======================================
  Hits         8204     8204           
  Misses        721      721           

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