perf(metrics): skip metrics computation when prometheus is disabled

Wrap histogram observation and SR set change detection with
Metrics.enabled() guard to avoid unnecessary computation (DB reads,
encode58Check, stream mapping, HashSet diff) on every block when
metrics are not enabled.

Author: warku123

framework/src/main/java/org/tron/core/metrics/blockchain/BlockChainMetricManager.java

@@ -177,30 +177,33 @@ public void applyBlock(BlockCapsule block) {
       Metrics.counterInc(MetricKeys.Counter.TXS, txCount,
           MetricLabels.Counter.TXS_SUCCESS, MetricLabels.Counter.TXS_SUCCESS);
     }
-    // Record transaction count distribution for all blocks (including empty blocks)
-    Metrics.histogramObserve(MetricKeys.Histogram.BLOCK_TRANSACTION_COUNT, txCount,
-        StringUtil.encode58Check(address));
-
-    // SR set change detection
-    long nextMaintenanceTime = dbManager.getDynamicPropertiesStore().getNextMaintenanceTime();
-    if (lastNextMaintenanceTime == -1) {
-      lastNextMaintenanceTime = nextMaintenanceTime;
-      lastActiveWitnesses.addAll(chainBaseManager.getWitnessScheduleStore().getActiveWitnesses()
-          .stream().map(w -> StringUtil.encode58Check(w.toByteArray()))
-          .collect(Collectors.toSet()));
-    } else if (nextMaintenanceTime != lastNextMaintenanceTime) {
-      Set<String> currentWitnesses = chainBaseManager.getWitnessScheduleStore().getActiveWitnesses()
-          .stream()
-          .map(w -> StringUtil.encode58Check(w.toByteArray()))
-          .collect(Collectors.toSet());
-      if (nextMaintenanceTime < lastNextMaintenanceTime) {
-        // Fork rollback detected — reinitialize instead of diffing
-        lastActiveWitnesses.clear();
-        lastActiveWitnesses.addAll(currentWitnesses);
-      } else {
-        recordSrSetChange(currentWitnesses);
+    if (Metrics.enabled()) {
+      // Record transaction count distribution for all blocks (including empty blocks)
+      Metrics.histogramObserve(MetricKeys.Histogram.BLOCK_TRANSACTION_COUNT, txCount,
+          StringUtil.encode58Check(address));
+
+      // SR set change detection
+      long nextMaintenanceTime = dbManager.getDynamicPropertiesStore().getNextMaintenanceTime();
+      if (lastNextMaintenanceTime == -1) {
+        lastNextMaintenanceTime = nextMaintenanceTime;
+        lastActiveWitnesses.addAll(chainBaseManager.getWitnessScheduleStore().getActiveWitnesses()
+            .stream().map(w -> StringUtil.encode58Check(w.toByteArray()))
+            .collect(Collectors.toSet()));
+      } else if (nextMaintenanceTime != lastNextMaintenanceTime) {
+        Set<String> currentWitnesses =
+            chainBaseManager.getWitnessScheduleStore().getActiveWitnesses()
+                .stream()
+                .map(w -> StringUtil.encode58Check(w.toByteArray()))
+                .collect(Collectors.toSet());
+        if (nextMaintenanceTime < lastNextMaintenanceTime) {
+          // Fork rollback detected — reinitialize instead of diffing
+          lastActiveWitnesses.clear();
+          lastActiveWitnesses.addAll(currentWitnesses);
+        } else {
+          recordSrSetChange(currentWitnesses);
+        }
+        lastNextMaintenanceTime = nextMaintenanceTime;
       }
-      lastNextMaintenanceTime = nextMaintenanceTime;
     }
   }