FIX: restore SciPy cost-function consistency

[rcjackson]

This fix restores consistency between the smoothness gradient and cost functions, and fixes an issue in the vertical vorticity cost function with mismatched axes. Written with assistance from GPT-Luna 5.6.

[codecov]

Codecov Report

❌ Patch coverage is 56.93069% with 87 lines in your changes missing coverage. Please review.
✅ Project coverage is 70.57%. Comparing base (2219015) to head (6572b81).
⚠️ Report is 7 commits behind head on main.

Files with missing lines	Patch %	Lines
pydda/cost_functions/_cost_functions_numpy.py	55.55%	32 Missing ⚠️
pydda/cost_functions/_cost_functions_jax.py	35.48%	20 Missing ⚠️
pydda/retrieval/wind_retrieve.py	42.85%	20 Missing ⚠️
pydda/cost_functions/cost_functions.py	65.11%	15 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #168      +/-   ##
==========================================
- Coverage   71.28%   70.57%   -0.71%     
==========================================
  Files          32       32              
  Lines        5509     5673     +164     
==========================================
+ Hits         3927     4004      +77     
- Misses       1582     1669      +87     

Flag	Coverage Δ
unittests	70.57% <56.93%> (-0.71%)	⬇️

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