[CodingBunny06]

Implement scientifically correct core fiber calculations with documented units, angle conventions, and strict physical-input validation.

• Physics
  • Add numerical aperture: sqrt(n_core² - n_cladding²).
  • Add critical angle in radians.
  • Add air-medium acceptance angle in radians.
  • Add total internal reflection detection using incidence angles measured from the interface normal.
• Validation
  • Reject invalid types, booleans, non-finite values, invalid refractive-index ordering, and out-of-range angles.
  • Treat equality with the critical angle as the TIR boundary, not TIR.
• Tests
  • Cover analytical reference values, normal and boundary cases, TIR/non-TIR behavior, and invalid inputs.

na = calculate_numerical_aperture(1.5, 1.4)
critical = calculate_critical_angle(1.5, 1.4)
acceptance = calculate_acceptance_angle(1.5, 1.4)
tir = is_total_internal_reflection(1.3, critical)

• Fixes #1 — Physics Engine: Core Fiber Calculations #1