When a MessageBatch is received, it may contain multiple retransmit requests. Currently, each message in the batch is processed one-by-one.

For example, when we have a number of messages, and one message has a retransmission request for messages [200..400], and another one has [300..400], then we're currently retransmitting 200 and then 100 messages (= 300), whereas these could be clubbed together to 200 messages.