Move the vignetting models into optika.radiometry

[roytsmart]

Summary

Folds the optika.vignetting subpackage into optika.radiometry. Vignetting (the relative field illumination) is itself a radiometric quantity, so it belongs alongside the effective-area model under one umbrella.

• AbstractVignettingModel, AbstractInterpolatedVignettingModel, and PolynomialVignettingModel now live in and are imported from optika.radiometry.
• The optika.vignetting subpackage is removed (and dropped from optika/__init__.py).
• Files moved via git mv (history preserved); the docstring example and tests updated to optika.radiometry.

Breaking change

optika.vignetting.PolynomialVignettingModel → optika.radiometry.PolynomialVignettingModel (and the two abstract classes likewise).

Testing

• pytest optika/radiometry/ — 33 passed; 100% coverage across all four radiometry files.
• Vignetting docstring example renders headless under optika.radiometry; black --check and ruff check clean.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.32%. Comparing base (19191f3) to head (893a9a8).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #160      +/-   ##
==========================================
- Coverage   99.32%   99.32%   -0.01%     
==========================================
  Files         117      116       -1     
  Lines        5771     5769       -2     
==========================================
- Hits         5732     5730       -2     
  Misses         39       39              

Flag	Coverage Δ
unittests	99.32% <100.00%> (-0.01%)	⬇️

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