Added SequentialSystem.vignetting(), a method to fit a polynomial vignetting model

[roytsmart]

Replaces #183, which GitHub closed when its base branch (feature/system-distortion, #181) was squash-merged and deleted; the branch is rebased onto main so only the vignetting commits remain.

Summary

• Add AbstractSequentialSystem.vignetting(), the vignetting counterpart of distortion(): the relative illumination at each scene coordinate is estimated from the fraction of unvignetted rays in the pupil, normalized so that its average over the field of view is unity, and fit with an optika.radiometry.PolynomialVignettingModel.
• Same interface as distortion(): custom wavelength/field/pupil grids (traced with rayfunction(), so grids left as None inherit the corresponding component of grid_input), normalized_field/normalized_pupil flags, polynomial degree, and a clear ValueError when the wavelength grid has no logical axis.
• The grid resolution and axis normalization shared between the two methods is factored into a private _rayfunction_and_axes() helper instead of duplicating ~30 lines.

Tests

test_vignetting mirrors test_distortion: parametrized over both grid sources and two polynomial degrees, asserting the model type, degree, the scalar-wavelength error branch, non-negative illumination, and that the illumination averages to unity over the field axes.

pytest optika/systems/_sequential_test.py -k "test_vignetting or test_distortion": 48 passed; black --check and ruff check clean.

🤖 Generated with Claude Code

https://claude.ai/code/session_01Lm9SxSpyNg9hx8dNL9pUXc

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.37%. Comparing base (db4ccce) to head (db21db6).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #184   +/-   ##
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  Coverage   99.37%   99.37%           
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  Files         116      116           
  Lines        6230     6257   +27     
=======================================
+ Hits         6191     6218   +27     
  Misses         39       39           

Flag	Coverage Δ
unittests	99.37% <100.00%> (+<0.01%)	⬆️

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