Add optika.vignetting.PolynomialVignettingModel

[roytsmart]

Summary

Adds the optika.vignetting subpackage for mapping scene coordinates (wavelength + field position) to the fraction of light transmitted by the optical system. Mirrors the structure of optika.distortion (#154).

• AbstractVignettingModel — defines the __call__(coordinates) -> scalar interface (the transmitted fraction) plus an inverse(coordinates) helper returning 1 / transmission (the vignetting-correction factor). inverse is defined on the abstract base since it only depends on the forward call.
• AbstractInterpolatedVignettingModel — adds the calibration-point interface (coordinates_scene, transmission, axis_wavelength, axis_field).
• PolynomialVignettingModel — fits a mean-centered polynomial to the measured transmission (center = scene.mean(axis_scene)), exposed via the public fit cached property, and provides plot_residual() to visualize the absolute fit residual vs. field angle with a subplot per wavelength (auto-sized figure, figsize/cmap/vmin/vmax arguments).

Registers the subpackage in optika/__init__.py.

Testing

• pytest optika/vignetting/_vignetting_test.py — 22 passed (call, inverse, fit, properties, and plot_residual across degree ∈ {1, 2}).
• 100% coverage on the new module; 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 99.31%. Comparing base (2a2fe34) to head (d285ab7).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #155      +/-   ##
==========================================
+ Coverage   99.29%   99.31%   +0.01%     
==========================================
  Files         111      114       +3     
  Lines        5537     5675     +138     
==========================================
+ Hits         5498     5636     +138     
  Misses         39       39              

Flag	Coverage Δ
unittests	99.31% <100.00%> (+0.01%)	⬆️

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