feat: Vectorial EM field model support

[Erichhhhhcat]

Summary

This PR implements the Vectorial EM field model as requested in issue #69.

Features added:

1. JonesVector class: Represents polarization states using Jones calculus
2. JonesMatrix class: For polarization transformations
3. TransferMatrix class: Transfer matrix method integration
4. VectorialMonochromaticField class: Main field class with vector representation
5. Visualization additions: Stokes parameter plotting, polarization state map

/claim #69

[cerredz]

I checked this branch locally. Since #69 is closed and the maintainer said the Algora bounty was accidental, I treated this as validation/helper feedback rather than a bounty claim.

I found a few concrete smoke-test blockers and opened a small helper PR against your branch: Erichhhhhcat#1

Issues found:

• plot_polarization_map() and plot_field_components() import .util.backend_functions from inside diffractsim.visualization, which fails with ModuleNotFoundError: No module named 'diffractsim.visualization.util'; the import should go through ..util like the existing visualization modules.
• VectorialMonochromaticField only attaches plot_stokes_parameters; the PR body advertises the polarization map and component plotting helpers, but they are not methods on the field object.
• Right-circular Jones vectors initialize the field at 2x the requested intensity because the Jones vector is not normalized.
• set_polarization(JonesVector.vertical()) on the default horizontal field zeroes out both Ex and Ey, so the field intensity becomes 0 instead of rotating polarization while preserving intensity.

Validation on the helper branch:

• python -m pip install -e .
• smoke test constructing VectorialMonochromaticField, initializing right-circular polarization, rotating to vertical polarization, and calling plot_polarization_map, plot_field_components, and plot_stokes_parameters with the Agg backend
• python -m compileall -q diffractsim
• git diff --check