Add GMAT interop tests for ocaml-cam
Tangential burn scenario from GMAT R2026a: ISS-like orbit + 0.1 km/s
prograde burn after 1 orbit. GMAT splits OEM into 2 segments at burn
epoch. 3 tests validate segment structure, velocity discontinuity (0.1
km/s delta-v, zero position change), and orbit raising (apogee increase).