Optional unitsUnits to reserve. Default 1.
Optional requireA reservation only an opted-in reconcile may settle once its lease runs out: a meter without resolveExpired
leaves it reserved and counted, so a legacy sweeper over the same tables cannot consume or release it. An explicit
settle() still settles it. Default false.
Optional nowThe clock, in epoch milliseconds; for tests.
The product's durable id for the request; a retry with the same id replays the reservation.