Implement Ionospheric Profiles Phase 3

[skyelaird]

Add complete ionospheric profile modeling capabilities including:

• CCIR/URSI coefficient maps (FourierMaps)
• E/F1/F2/Es layer parameter calculations
• Electron density profile modeling
• Ionogram generation
• True and virtual height calculations
• Penetration angle calculations

New modules:

• fourier_maps.py: CCIR/URSI data loading and interpolation
• ionospheric_profile.py: Electron density and ionogram modeling
• layer_parameters.py: Layer parameter computation

Features:

• Load and interpolate monthly coefficient files
• Compute critical frequencies (foE, foF1, foF2, foEs)
• Model electron density vs height profiles
• Calculate true and virtual heights for any frequency
• Generate ionograms with E, F1, and F2 layer cusps
• Compute penetration angles for oblique propagation
• Support seasonal and solar cycle variations

Testing:

• Comprehensive test suite with 20+ tests
• Integration tests for full workflow
• Validation against expected ionospheric values

Version: 0.3.0 (60% complete)