KAFKA-15085: Make Timer.java implement AutoCloseable (#13872)

Change Timer.java to implement AutoCloseable because automatic bug finders will flag a warning if an object of a class is marked as AutoCloseable but is not closed properly in the code.

Reviewers:  Divij Vaidya <diviv@amazon.com>

core/src/main/scala/kafka/raft/RaftManager.scala

@@ -195,7 +195,7 @@ class KafkaRaftManager[T](
 
   def shutdown(): Unit = {
     CoreUtils.swallow(expirationService.shutdown(), this)
-    CoreUtils.swallow(expirationTimer.shutdown(), this)
+    CoreUtils.swallow(expirationTimer.close(), this)
     CoreUtils.swallow(raftIoThread.shutdown(), this)
     CoreUtils.swallow(client.close(), this)
     CoreUtils.swallow(scheduler.shutdown(), this)

core/src/main/scala/kafka/server/DelayedOperation.scala

@@ -339,7 +339,7 @@ final class DelayedOperationPurgatory[T <: DelayedOperation](purgatoryName: Stri
       })
       expirationReaper.awaitShutdown()
     }
-    timeoutTimer.shutdown()
+    timeoutTimer.close()
     metricsGroup.removeMetric("PurgatorySize", metricsTags)
     metricsGroup.removeMetric("NumDelayedOperations", metricsTags)
   }

core/src/test/scala/unit/kafka/utils/timer/MockTimer.scala

@@ -67,6 +67,6 @@ class MockTimer(val time: MockTime = new MockTime) extends Timer {
 
   def size: Int = taskQueue.size
 
-  override def shutdown(): Unit = {}
+  override def close(): Unit = {}
 
 }

server-common/src/main/java/org/apache/kafka/server/util/timer/SystemTimer.java

@@ -106,7 +106,8 @@ public class SystemTimer implements Timer {
         return taskCounter.get();
     }
 
-    public void shutdown() {
+    @Override
+    public void close() {
         taskExecutor.shutdown();
     }
 }

server-common/src/main/java/org/apache/kafka/server/util/timer/Timer.java

@@ -16,7 +16,7 @@
  */
 package org.apache.kafka.server.util.timer;
 
-public interface Timer {
+public interface Timer extends AutoCloseable {
     /**
      * Add a new task to this executor. It will be executed after the task's delay
      * (beginning from the time of submission)
@@ -38,8 +38,4 @@ public interface Timer {
      */
     int size();
 
-    /**
-     * Shutdown the timer service, leaving pending tasks unexecuted
-     */
-    void shutdown();
 }

server-common/src/test/java/org/apache/kafka/server/util/timer/TimerTest.java

@@ -74,8 +74,8 @@ public class TimerTest {
     }
 
     @AfterEach
-    public void teardown() {
-        timer.shutdown();
+    public void teardown() throws Exception {
+        timer.close();
     }
 
     @Test