Track message delivery state in QueueMessageReference #1797
Description
Add a delivered flag to QueueMessageReference to distinguish between messages that are pending dispatch and messages that have been dispatched to a consumer but
not yet acknowledged.
Currently, once a message is dispatched to a consumer, there is no way to know whether the consumer has confirmed receipt (via delivered ack) or if the message is
still in-flight. This adds a delivered boolean that is set to true when processing DeliveredAck in PrefetchSubscription, enabling better visibility into message
lifecycle state.