Add optical raytracing example

[Littie28]

Summary

Adds Example 04 demonstrating advanced coordinate frame usage in optical raytracing. This example showcases how frame transformations dramatically simplify optical system design by allowing lens repositioning and reorientation
with single-line changes while keeping all geometric algorithms unchanged.

What's included

New notebook: examples/04-simple-raytracing.ipynb

• Complete raytracing implementation with frame-based coordinates
• Spherical and hyperbolic lens surface profiles
• Meridional plane reduction technique for axisymmetric surfaces
• Visualization of optical aberrations (spherical aberration, coma)
• Immutable Ray class following hazy design philosophy
• Snell's law vector-form refraction
• Numerical intersection finding with scipy.optimize.brentq

Key demonstrations

1. Frame transformations simplify optics: Reposition/rotate entire optical system by modifying frame definitions - all geometric calculations (intersection, refraction, propagation) remain unchanged
2. Interchangeable components: Swap lens profiles (spherical -> hyperbolic) by changing one function - the raytracing algorithm stays identical
3. Real-world techniques: Uses meridional plane reduction and conic surface formulas

Educational structure

• TL;DR section for quick value proposition
• Three progressive examples: aligned lens, misaligned lens (coma), hyperbolic lens
• Comprehensive takeaways explaining frame-based coordinate benefits
• Visualizations: 3D ray traces + 2D footprint plots

Changes

• Created examples/04-simple-raytracing.ipynb
• Updated CHANGELOG.md with new example entries

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