Refactor test_hybrid_burns: qualitative→quantitative checks with named tolerances
- Update precalc script: add after_1_a for multi-burn, three-burn plane change
- Convert 17 qualitative checks (> , <, != 0) to quantitative WithinAbs()
- Replace hardcoded tolerances: A_TOL, E_TOL, D_TOL, M_TOL, ANG_TOL, R_TOL
- Remove unused init_els variable
- Keep rel_err thresholds at 0.01 (continuous burn approximation tolerance)
- All 932 assertions pass across 25 test cases (no regressions)