[ISSUE #10580] Clarify static topic epoch comparison intent

Address review feedback on PR #10581: explain why the epoch comparison
in ClientMetadata.topicRouteData2EndpointsForStaticTopic changed from
>= to >. The change is intentional — total queue count is now scoped to
the latest epoch so a stale mapping cannot inflate maxTotalNums, with
same-epoch ties broken by the largest totalQueues (covered by the
UsesMaxTotalQueuesInSameEpoch test). Also document why the sort uses an
overflow-safe comparator.

Co-Authored-By: Claude <noreply@anthropic.com>

Author: Aias00

remoting/src/main/java/org/apache/rocketmq/remoting/rpc/ClientMetadata.java

@@ -120,12 +120,18 @@ public static ConcurrentMap<MessageQueue, String> topicRouteData2EndpointsForSta
             Map<String, TopicQueueMappingInfo> topicQueueMappingInfoMap =  mapEntry.getValue();
             ConcurrentMap<MessageQueue, TopicQueueMappingInfo> mqEndPoints = new ConcurrentHashMap<>();
             List<Map.Entry<String, TopicQueueMappingInfo>> mappingInfos = new ArrayList<>(topicQueueMappingInfoMap.entrySet());
+            // Sort mappings by epoch descending, so the newest epoch is visited first.
+            // Subtracting long epochs and casting to int overflows when the epoch gap exceeds
+            // Integer.MAX_VALUE and reverses the ordering, so use an overflow-safe comparison.
             mappingInfos.sort(Comparator.comparingLong(
                 (Map.Entry<String, TopicQueueMappingInfo> entry) -> entry.getValue().getEpoch()).reversed());
             int maxTotalNums = 0;
             long maxTotalNumOfEpoch = -1;
             for (Map.Entry<String, TopicQueueMappingInfo> entry : mappingInfos) {
                 TopicQueueMappingInfo info = entry.getValue();
+                // Scope total queue count to the latest epoch only: a stale mapping must not
+                // inflate maxTotalNums beyond what the newest epoch advertises. Among mappings
+                // sharing that latest epoch, keep the largest total queue count.
                 if (info.getEpoch() > maxTotalNumOfEpoch) {
                     maxTotalNumOfEpoch = info.getEpoch();
                     maxTotalNums = info.getTotalQueues();