Add optika.distortion.PolynomialDistortionModel which can interpolate between object and sensor coordinates.

[roytsmart]

Summary

Adds the optika.distortion subpackage for mapping scene coordinates (wavelength + field position) to sensor coordinates and back.

• AbstractDistortionModel — defines the distort/undistort interface. Distortion carries wavelength alongside position (the scene→sensor mapping generally depends on wavelength, e.g. spectrograph dispersion), so the two methods are inverses only up to model accuracy.
• AbstractInterpolatedDistortionModel — adds the calibration-point interface (coordinates_scene, coordinates_sensor, axis_wavelength, axis_field).
• PolynomialDistortionModel — fits separate forward and inverse polynomials via na.PolynomialFitFunctionArray, using a mean-centered reference (center=inputs.mean(...)) for numerical conditioning. The underlying fits are exposed as the public fit/fit_inverse cached properties for introspection (coefficients, rms, etc.).

Registers the subpackage in optika/__init__.py.

Notes

This factors the distortion concept into a reusable object. The inline polynomial-distortion logic in systems/_interpolated.py (distortion/distortion_inverse) is a natural follow-up to migrate onto this abstraction.

Testing

• pytest optika/distortion/_distortion_test.py — 22 passed (round-trip, type, and fit-introspection tests across degree ∈ {1, 2}).
• 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 99.29%. Comparing base (22a9629) to head (ccc1d2a).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #154      +/-   ##
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+ Coverage   99.27%   99.29%   +0.01%     
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  Files         108      111       +3     
  Lines        5391     5537     +146     
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+ Hits         5352     5498     +146     
  Misses         39       39              

Flag	Coverage Δ
unittests	99.29% <100.00%> (+0.01%)	⬆️

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