ReactiveMessagePipelineTest.handlingTimeout continues to be flaky

[lhotari]

Example failure:

  Test handlingTimeout() FAILED

  java.lang.AssertionError: 
  Expected size: 9 but was: 8 in:
  [123456:4044:-1,
      123456:4045:-1,
      123456:4046:-1,
      123456:4047:-1,
      123456:4048:-1,
      123456:4051:-1,
      123456:4052:-1,
      123456:4053:-1]
      at org.apache.pulsar.reactive.client.api.ReactiveMessagePipelineTests.handlingTimeout(ReactiveMessagePipelineTests.java:221)


    [2025-05-20 10:06:41,684] [parallel-2] [org.apache.pulsar.reactive.client.internal.api.DefaultReactiveMessagePipeline] ERROR Message handling for message id 123456:4049:-1 failed.
    java.util.concurrent.TimeoutException: Did not observe any item or terminal signal within 5ms in 'source(MonoDefer)' (and no fallback has been configured)
    	at reactor.core.publisher.FluxTimeout$TimeoutMainSubscriber.handleTimeout(FluxTimeout.java:296) [reactor-core-3.6.16.jar:3.6.16]
    	at reactor.core.publisher.FluxTimeout$TimeoutMainSubscriber.doTimeout(FluxTimeout.java:281) [reactor-core-3.6.16.jar:3.6.16]
    	at reactor.core.publisher.FluxTimeout$TimeoutTimeoutSubscriber.onNext(FluxTimeout.java:420) [reactor-core-3.6.16.jar:3.6.16]
    	at reactor.core.publisher.FluxOnErrorReturn$ReturnSubscriber.onNext(FluxOnErrorReturn.java:162) [reactor-core-3.6.16.jar:3.6.16]
    	at reactor.core.publisher.MonoDelay$MonoDelayRunnable.propagateDelay(MonoDelay.java:270) [reactor-core-3.6.16.jar:3.6.16]
    	at reactor.core.publisher.MonoDelay$MonoDelayRunnable.run(MonoDelay.java:285) [reactor-core-3.6.16.jar:3.6.16]
    	at reactor.core.scheduler.SchedulerTask.call(SchedulerTask.java:68) [reactor-core-3.6.16.jar:3.6.16]
    	at reactor.core.scheduler.SchedulerTask.call(SchedulerTask.java:28) [reactor-core-3.6.16.jar:3.6.16]
    	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264) [?:?]
    	at java.base/java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:304) [?:?]
    	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136) [?:?]
    	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635) [?:?]
    	at java.base/java.lang.Thread.run(Thread.java:840) [?:?]
    [2025-05-20 10:06:41,690] [parallel-4] [org.apache.pulsar.reactive.client.internal.api.DefaultReactiveMessagePipeline] ERROR Message handling for message id 123456:4050:-1 failed.
    java.util.concurrent.TimeoutException: Did not observe any item or terminal signal within 5ms in 'source(MonoDefer)' (and no fallback has been configured)
    	at reactor.core.publisher.FluxTimeout$TimeoutMainSubscriber.handleTimeout(FluxTimeout.java:296) [reactor-core-3.6.16.jar:3.6.16]
    	at reactor.core.publisher.FluxTimeout$TimeoutMainSubscriber.doTimeout(FluxTimeout.java:281) [reactor-core-3.6.16.jar:3.6.16]
    	at reactor.core.publisher.FluxTimeout$TimeoutTimeoutSubscriber.onNext(FluxTimeout.java:420) [reactor-core-3.6.16.jar:3.6.16]
    	at reactor.core.publisher.FluxOnErrorReturn$ReturnSubscriber.onNext(FluxOnErrorReturn.java:162) [reactor-core-3.6.16.jar:3.6.16]
    	at reactor.core.publisher.MonoDelay$MonoDelayRunnable.propagateDelay(MonoDelay.java:270) [reactor-core-3.6.16.jar:3.6.16]
    	at reactor.core.publisher.MonoDelay$MonoDelayRunnable.run(MonoDelay.java:285) [reactor-core-3.6.16.jar:3.6.16]
    	at reactor.core.scheduler.SchedulerTask.call(SchedulerTask.java:68) [reactor-core-3.6.16.jar:3.6.16]
    	at reactor.core.scheduler.SchedulerTask.call(SchedulerTask.java:28) [reactor-core-3.6.16.jar:3.6.16]
    	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264) [?:?]
    	at java.base/java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:304) [?:?]
    	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136) [?:?]
    	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635) [?:?]
    	at java.base/java.lang.Thread.run(Thread.java:840) [?:?]
    [2025-05-20 10:06:41,698] [parallel-3] [org.apache.pulsar.reactive.client.internal.api.DefaultReactiveMessagePipeline] ERROR ReactiveMessageHandler was unexpectedly completed.