KAFKA-17554 Flaky testFutureCompletionOutsidePoll in ConsumerNetworkClientTest (#18298)

Jira: https://issues.apache.org/jira/browse/KAFKA-17554

In the previous workflow, the test passes under two conditions:

1. The `t1` thread is waiting for the main thread's `client.wakeup()`.
If successful, `t1` will wake up `t2`, allowing `t2` to complete the
future.
2. If `t1` fails to receive the `client.wakeup()` from the main thread,
`t2` will be woken up by the main thread.

In the previous implementation, we used a `CountDownLatch` to control
the execution of three threads, but it often led to race conditions.
Currently, we have modified it to use two threads to test this scenario.

I run `I=0;  while ./gradlew :clients:test --tests
ConsumerNetworkClientTest.testFutureCompletionOutsidePoll --rerun
--fail-fast; do  (( I=$I+1 )); echo "Completed run: $I"; sleep 1; done`
and pass 3000+ times.

![image](https://github.com/user-attachments/assets/3b8d804e-fbe0-4030-8686-4960fc717d07)

Reviewers: Chia-Ping Tsai <chia7712@gmail.com>

clients/src/test/java/org/apache/kafka/clients/consumer/internals/ConsumerNetworkClientTest.java

@@ -41,7 +41,6 @@ import org.apache.kafka.common.utils.LogContext;
 import org.apache.kafka.common.utils.MockTime;
 import org.apache.kafka.test.TestUtils;
 
-import org.junit.jupiter.api.Disabled;
 import org.junit.jupiter.api.Test;
 
 import java.time.Duration;
@@ -266,45 +265,34 @@ public class ConsumerNetworkClientTest {
         assertEquals(metadataException, exc);
     }
 
-    @Disabled("KAFKA-17554")
     @Test
     public void testFutureCompletionOutsidePoll() throws Exception {
         // Tests the scenario in which the request that is being awaited in one thread
         // is received and completed in another thread.
-        
-        final CountDownLatch t1TheardCountDownLatch = new CountDownLatch(1);
-        final CountDownLatch t2ThreadCountDownLatch = new CountDownLatch(2);
-
         final RequestFuture<ClientResponse> future = consumerClient.send(node, heartbeat());
         consumerClient.pollNoWakeup(); // dequeue and send the request
 
+        CountDownLatch bothThreadsReady = new CountDownLatch(2);
+
         client.enableBlockingUntilWakeup(2);
+
         Thread t1 = new Thread(() -> {
-            t1TheardCountDownLatch.countDown();
+            bothThreadsReady.countDown();
             consumerClient.pollNoWakeup();
-            t2ThreadCountDownLatch.countDown();
+        });
+
+        Thread t2 = new Thread(() -> {
+            bothThreadsReady.countDown();
+            consumerClient.poll(future);
         });
 
         t1.start();
-
-        Thread t2 = new Thread(() -> {
-            try {
-                t2ThreadCountDownLatch.await();
-                consumerClient.poll(future);
-            } catch (InterruptedException e) {
-                throw new RuntimeException(e);
-            }
-        });
         t2.start();
 
-        // Simulate a network response and return from the poll in t1
+        // Wait until both threads are blocked in poll
+        bothThreadsReady.await();
         client.respond(heartbeatResponse(Errors.NONE));
-        // Wait for t1 to block in poll
-        t1TheardCountDownLatch.await();
-        
         client.wakeup();
-        // while t1 is blocked in poll, t2 should be able to complete the future
-        t2ThreadCountDownLatch.countDown();
 
         // Both threads should complete since t1 should wakeup t2
         t1.join();