Removed redundant calculations, unneeded array allocations from jump step

[t-brandt]

Resolves JP-3697

Closes #

This PR affects the two-point-difference jump step only. It removes duplicate and redundant calculations and unneeded array allocations, which make a significant difference for large uncal files. Masked array median is also changed to nanmedian, and a few variables are renamed to avoid overwriting a quantity that is needed at the end of the routine.

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>/stcal@<branch>")
  • [ ] jwst regression test
  • [ ] romancal regression test

news fragment change types...

- ``changes/.apichange.rst``: change to public API - ``changes/.bugfix.rst``: fixes an issue - ``changes/.general.rst``: infrastructure or miscellaneous change

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 85.18%. Comparing base (5f94030) to head (768dad4). Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #302 +/- ## ========================================== - Coverage 85.19% 85.18% -0.02% ========================================== Files 46 46 Lines 8804 8797 -7 ========================================== - Hits 7501 7494 -7 Misses 1303 1303 ```

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[ddavis-stsci]

The romancal tests for these changes pass, https://github.com/spacetelescope/RegressionTests/actions/runs/11328631054