MINOR: Collection/Option usage simplification via methods introduced in Java 9 & 11 (#18305)

Relevant methods:
1. `List.of`, `Set.of`, `Map.of` and similar (introduced in Java 9)
2. Optional: `isEmpty` (introduced in Java 11), `stream` (introduced in Java 9).

Reviewers: Mickael Maison <mimaison@users.noreply.github.com>

Author: ijuma

clients/src/main/java/org/apache/kafka/clients/NetworkClient.java

@@ -1219,7 +1219,7 @@ public long maybeUpdate(long now) {
                 return metadataTimeout;
             }
 
-            if (!metadataAttemptStartMs.isPresent())
+            if (metadataAttemptStartMs.isEmpty())
                 metadataAttemptStartMs = Optional.of(now);
 
             // Beware that the behavior of this method and the computation of timeouts for poll() are
@@ -1412,7 +1412,7 @@ private long maybeUpdate(long now, Node node) {
             if (canSendRequest(nodeConnectionId, now)) {
                 Optional<AbstractRequest.Builder<?>> requestOpt = clientTelemetrySender.createRequest();
 
-                if (!requestOpt.isPresent())
+                if (requestOpt.isEmpty())
                     return Long.MAX_VALUE;
 
                 AbstractRequest.Builder<?> request = requestOpt.get();

clients/src/main/java/org/apache/kafka/common/Uuid.java

@@ -20,8 +20,6 @@
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Base64;
-import java.util.Collections;
-import java.util.HashSet;
 import java.util.List;
 import java.util.Set;
 
@@ -51,11 +49,7 @@ public class Uuid implements Comparable<Uuid> {
     /**
      * The set of reserved UUIDs that will never be returned by the randomUuid method.
      */
-    public static final Set<Uuid> RESERVED = Collections.unmodifiableSet(new HashSet<>(Arrays.asList(
-            METADATA_TOPIC_ID,
-            ZERO_UUID,
-            ONE_UUID
-    )));
+    public static final Set<Uuid> RESERVED = Set.of(ZERO_UUID, ONE_UUID);
 
     private final long mostSignificantBits;
     private final long leastSignificantBits;