Add vectorial EM field simulator with polarization support

[SolariSystems]

Summary

I've implemented vectorial electromagnetic field representation with full polarization support for diffractsim, addressing Issue #69.

Features Added

1. VectorialField class - Extends scalar field handling to support vectorial (Ex, Ey) components
2. Jones calculus:
   • JonesVector - Polarization state representation (horizontal, vertical, diagonal, circular)
   • JonesMatrix - Optical elements (polarizers, half-wave plates, quarter-wave plates, general waveplates)
3. Stokes parameters - Full S0, S1, S2, S3 computation at each spatial point
4. Propagation - Angular spectrum method applied independently to both polarization components
5. Helper functions - create_polarized_beam(), apply_polarization_element()

Files

• diffractsim/vectorial_simulator.py (NEW) - Core implementation (~500 lines)
• diffractsim/__init__.py (MODIFIED) - Exports new classes
• examples/vectorial_polarization_example.py (NEW) - Usage demonstrations

Usage Example

from diffractsim import VectorialField, create_polarized_beam, apply_polarization_element
from diffractsim import mm, nm, cm

# Create circularly polarized beam
field = create_polarized_beam(632.8*nm, 10*mm, 10*mm, 256, 256, 
                              polarization='right_circular')

# Apply quarter-wave plate
apply_polarization_element(field, 'quarter_wave', angle=0)

# Get Stokes parameters
S0, S1, S2, S3 = field.get_stokes_parameters()

# Propagate
field.propagate(10*cm)

References

• Jones, R. C. (1941). A new calculus for the treatment of optical systems. JOSA, 31(7), 488-493.
• Born, M., & Wolf, E. (1999). Principles of optics. Cambridge University Press.

/claim 69