Move all shared tolerance constants to src/test_utilities.h with inline
comments. Update all test files to use header constants instead of local
definitions. Add DRIFT_TOL for parabolic orbit energy checks.
Key changes:
- test_utilities.h: consolidated constants with inline descriptions,
removed per-test doc comments, added DRIFT_TOL=1e-12
- test_cartesian_to_elements_advanced.cpp: use header E_TOL, ANG_TOL,
A_TOL; local A_TOL_LARGE=2e-4 for |a|=1e11 vis-viva error cases
- test_parabolic_orbit.cpp: use V_TOL, E_TOL, REL_TOL, R_TOL, DRIFT_TOL;
add precalculated initial velocity check; remove FIXME ratio test
- test_cartesian_to_elements_basic.cpp, test_extreme_eccentricity.cpp,
test_extreme_orientation_mixed.cpp, test_extreme_timescales.cpp:
migrate remaining local constants to header
- continue.md: update tolerance reference table to match header
- scripts/precalc_parabolic_orbit.py: remove velocity sampling loop
(no longer used by C++ test)
All 624 tests pass.