Strategy that allows to delay any action when cancelStage is invoked.

The idea of this strategy is to delay any action on cancellation because it is expected that the stage is completed through another path in the meantime. The downside is that a stage and a stream may live longer than expected if no such signal is received and cancellation is invoked later on. In streams with many stages that all apply this strategy, this strategy might significantly delay the propagation of a cancellation signal because each upstream stage might impose such a delay. During this time, the stream will be mostly "silent", i.e. it cannot make progress because of backpressure, but you might still be able observe a long delay at the ultimate source.