[Bug] Some transports block on a delayed requeue where not natively supported

[iancooper]

Describe the bug

Our API offers a delayed requeue where it is possible that the error is transient and could be fixed by simply returning to the queue with a delay. There are three responses we have:

1. Native support for requeue with delay; we used this
2. No native support for requeue and we requeue via a timer event that posts after the elapsed time window
3. We block for the delay period then requeue

We know that 3 is never the right solution as this will block the whole pump, and pause message processing, not requeue with a delay. We should fix those transports that have the incorrect behavior.

Further technical details

• The internal message consumer is a good example of how to get this right with a internal Requeue method that is called via a timer if delay is requested, and just passed through if not.