feat: use a rolling timer rather than a simple time.Ticker in batch consumer

[Abdulsametileri]

Rolling Timer

• Use time.NewTimer(...) instead of time.NewTicker(...)
• Reset this timer every time you receive a message (to extend the flush deadline).
• If the timer expires (i.e., case <-flushTimer.C:), flush whatever messages have accumulated.

That way, for “hot” topics (lots of messages in short intervals), the timer keeps resetting and you primarily flush on message-count/byte-size constraints. For slower topics, you’ll flush after no new messages arrive within messageGroupDuration.

[Abdulsametileri]

implemented, and currently I am testing
#156