Get the demurrage and detention clocks of a shipment

Use this to answer "how many free days are left on this shipment" or "what will demurrage cost us". Returns one demurrage clock and one detention clock per container, plus the clock that matters most right now (active_clock). Clocks only exist for ocean shipments, for each container that has loading, discharge, gate-out or empty-return events, and stay not_started until the container is discharged; for any other shipment the clock lists are empty and active_clock is null. Free days come from the shipment itself, the latest arrival notice, or the organization's carrier terms, in that order (see free_days_source).