ECSS Simulation Modelling — Epoch Time (space-systems/ecss/e4008-epoch-time)

Convert an epoch-scale schedule entry onto simulation time under ECSS-E-ST-40-08C clause 5.4.1, the single normative item that clause places on an entry written at an absolute instant. Use when a schedule mixes epoch instants with simulation-time offsets and the simulator has to decide when each entry actually fires: subtracting the declared epoch at simulation time zero, refusing a float nanosecond count and an undeclared epoch reference, keeping the conversion exactly reversible, reporting an instant the run has already passed instead of dropping it, and stepping a repeating entry to its first occurrence at or after the resolution instant. Trigger: ecss, e-st-40-08-simu…