In check_maneuver_trigger() (true-anomaly branch), eliminate the
propagate_orbital_elements() look-ahead probe that was called every
frame for pending maneuvers. Replace with direct analytical computation
of dt_needed from mean anomaly delta.
Benefits:
- Eliminates ~24k redundant Kepler solves per Hohmann transfer wait
period (DT=10s, 244k s wait time)
- More precise: no discretization error from single-step propagation
- Simpler logic: removed angle_between check, wraparound detection
- Removes dead angle_between() helper function
Elliptical orbits only — added TODO for parabolic/hyperbolic support.
All 154 tests pass (240,445 assertions).
cinnaboot