Ruimin MA

### Motivation This PR addresses a potential NullPointerException (NPE) that could occur when calling the `seek()` method with a `TopicMessageIdImpl` that has a null topic. ### Modifications 1. Added null...

[improve][broker] Use atomic counter for ongoing transaction count

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### Motivation Currently, `txnMetaMap.size()` is used to determine if a new transaction can be added and for metrics reporting. However, `txnMetaMap` is a `ConcurrentSkipListMap`, and calling `size()` is an O(n)...

### Motivation When a client sends an individual acknowledgment for a message that does not exist in the pending acknowledgment list (e.g., due to deletion or expiration), the method `getAckOwnerConsumerAndBatchSize`...