A Nursery is a place for senders to be ran in, while being a Sender itself. Stopping the Nursery cancels all senders. When any Sender completes with an Error all Senders are canceled as well. Cancellation is signaled with a StopToken. Senders themselves bare the responsibility to respond to stop requests. When cancellation happens all Senders are waited on for completion. Senders can be added to the Nursery at any time. Senders are only started when the Nursery itself is being awaited on.