Stage 01: ASTRONOMICAL_TIME — establish the moment in astronomical time.
Appends time scale conversions to the snapshot for downstream stages.
@type t() :: %EphCore.SnapshotPipeline.AstronomicalTime{ delta_t_seconds: float(), delta_t_source: atom(), jd_tt: float(), jd_ut1: float(), jd_utc: float() }
@spec resolve(term()) :: term()