Disable batch receive timer for Readers (apache#8381)

- since the Reader implementation doesn't use the batch receiving
  functionality, it's more efficient to set the timeout to 0 of the
  BatchReceivePolicy of the internal consumer of the Reader
  implementation
  - this disables the timer that would get called every 100ms by default
    just for nothing

pulsar-client/src/main/java/org/apache/pulsar/client/impl/ReaderImpl.java

@@ -31,7 +31,10 @@
 import org.apache.pulsar.common.naming.TopicName;
 
 public class ReaderImpl<T> implements Reader<T> {
-
+    private static final BatchReceivePolicy DISABLED_BATCH_RECEIVE_POLICY = BatchReceivePolicy.builder()
+            .timeout(0, TimeUnit.MILLISECONDS)
+            .maxNumMessages(1)
+            .build();
     private final ConsumerImpl<T> consumer;
 
     public ReaderImpl(PulsarClientImpl client, ReaderConfigurationData<T> readerConfiguration,
@@ -50,6 +53,10 @@ public ReaderImpl(PulsarClientImpl client, ReaderConfigurationData<T> readerConf
         consumerConfiguration.setReceiverQueueSize(readerConfiguration.getReceiverQueueSize());
         consumerConfiguration.setReadCompacted(readerConfiguration.isReadCompacted());
 
+        // Reader doesn't need any batch receiving behaviours
+        // disable the batch receive timer for the ConsumerImpl instance wrapped by the ReaderImpl
+        consumerConfiguration.setBatchReceivePolicy(DISABLED_BATCH_RECEIVE_POLICY);
+
         if (readerConfiguration.getReaderName() != null) {
             consumerConfiguration.setConsumerName(readerConfiguration.getReaderName());
         }