there are two leaks here:
* QueueImpl::delivery might create a new iterator if a delivery happens right after a consumer was removed, and that iterator might belog to a consumer that was already closed
as a result of that, the iterator may leak messages and hold references until a reboot is done. I have seen scenarios where messages would not be dleivered because of this.
* ProtonTransaction holding references: the last transaction might hold messages in the memory longer than expected. In tests I have performed the messages were accumulating in memory. and I cleared it here.
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