registerDestination

Create the per-destination shipment / weight / cube counters for sender if they do not yet exist. KSL forbids new ModelElements after the executive starts, so this is a construction-time operation. Call it for any destination that may receive a shipment under immediateTransportFlag without a configured transport time — otherwise the per-destination counters never get created and the increments in transportDemand silently no-op (audit finding D). setTransportTime already calls this.