LoomKafkaProducer|Consumer let the background thread finish itself

[maschmid]

Follows up to #3957 , but for LoomKafkaProducer, and unifies the approach

Instead of interrupting the BlockingQueue::take, we just use poll in the background thread, so we don't have to deal with interrupting the thread, so we now don't accidentally interrupt the actual processing of the queued tasks.

Instead of waiting for the Thread to be marked as "finished", we just wait by Thread::join. The only way it would block forever, is if the processing of the task would wait forever.

Proposed Changes

• 🧹 LoomKafkaProducer|Consumer let the background thread finish itself

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 48.25%. Comparing base (961961c) to head (7eb9c2a).
Report is 31 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4013   +/-   ##
=======================================
  Coverage   48.25%   48.25%           
=======================================
  Files         246      246           
  Lines       14540    14540           
=======================================
  Hits         7016     7016           
  Misses       6817     6817           
  Partials      707      707           

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[maschmid]

actually, we still need to interrupt the eventQueue.take()

[maschmid]

/test channel-integration-tests-ssl

https://prow.knative.dev/view/gs/knative-prow/pr-logs/pull/knative-extensions_eventing-kafka-broker/4013/channel-integration-tests-ssl_eventing-kafka-broker_main/1817914303898980352

TestEventTransformationForSubscription looks like same error as in yesterdays nightly https://prow.knative.dev/view/gs/knative-prow/logs/nightly_eventing-kafka-broker_main_periodic/1817493539722891264 , assuming flake

[maschmid]

/test upgrade-tests

[maschmid]

/test reconciler-tests-namespaced-broker
/test upgrade-tests

[matzew]

/test reconciler-tests-namespaced-broker

[pierDipi]

/lgtm
/approve

[knative-prow]

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