fix mk_level2_image for 3d shape

[braingram]

I initially hoped to drop the 3d shape input. However the maker_utils tests are quite tied to the current structure and it wasn't immediately obvious how to drop the 3d input without breaking several other tests (which provide a 3d shape).

Instead this PR takes the approach of fixing the 3d shape input handling and adds a regression test for the issue.

Closes #377

Regression tests running at https://github.com/spacetelescope/RegressionTests/actions/runs/10405495032

Checklist

• Added entry in CHANGES.rst under the corresponding subsection
• updated relevant tests
• updated relevant documentation
• Passed romancal regression testing on Jenkins / PLWishMaster. Link: https://plwishmaster.stsci.edu:8081/job/RT/job/romancal/XXX/

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.68%. Comparing base (087a60d) to head (80c2f6e).
Report is 69 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #378      +/-   ##
==========================================
+ Coverage   97.56%   97.68%   +0.12%     
==========================================
  Files          30       37       +7     
  Lines        2788     3370     +582     
==========================================
+ Hits         2720     3292     +572     
- Misses         68       78      +10     

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[schlafly]

LGTM, thanks Brett!