[fix] [broker] Fix negative subscription/consumer's unack-messages

[poorbarcode]

Motivation

Issue: negative unack-messages

• Consumer-1 received messages.
• Unload the topic.
• The message may be sent to consumer-2, but the consumption of consumer-1 is still in progress now.
• Consumer-1 and consumer-2 acknowledge the message concurrently.

unack-messages may be reduced twice in above scenario, you can reproduce the issue by the new test testAcknowledgeConcurrently

Modifications

• Only reduce unack-messages who actually deleted messages successfully.
• This PR also fixes the issue of the unack-messages is not accurate
• The current PR does not fix the same issue when enable TXN, we need a separate PR to fix it

Documentation

• [ ] doc
• [ ] doc-required
• [x] doc-not-needed
• [ ] doc-complete

Matching PR in forked repository

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