AsyncKafkaConsumer cannot reliably leave group when closed with small timeout

If close() is called with a short timeout (e.g. 0 ms), the process cannot complete, leading to the consumer remaining in the consumer group.

On close(), the consumer attempts to unsubscribe and leave the consumer group. This process requires hops back and forth between the application and background threads to call the ConsumerRebalanceListener. Those hops add a nonzero amount of time to the close step.

The events used to communicate between the application and background threads are based on the timeout provided by the user. If the timeout is not sufficient, the events will expire, and the process will be left incomplete.