fix(metrics): snapshot MetricData points before export to prevent AIOOBE

The OTel SDK's NumberDataPointMarshaler.createRepeated allocates an
array based on points.size() then iterates. If callback threads
concurrently add data points between size() and iteration, an
ArrayIndexOutOfBoundsException occurs. This adds a defensive snapshot
of all data point collections at the start of export(), ensuring
the delegate exporter always receives immutable point collections.

Author: Houlong66

broker/src/main/java/org/apache/rocketmq/broker/metrics/BatchSplittingMetricExporter.java

@@ -115,21 +115,26 @@ public CompletableResultCode export(
             return delegate.export(metrics);
         }
 
+        // Snapshot to avoid concurrent-modification AIOOBE
+        // in OTel SDK marshaling (see NumberDataPointMarshaler)
+        List<MetricData> snapshotted =
+            snapshotAllMetrics(metrics);
+
         int maxBatchSize =
             maxBatchSizeSupplier.getAsInt();
 
         int totalDataPoints = 0;
-        for (MetricData md : metrics) {
+        for (MetricData md : snapshotted) {
             totalDataPoints +=
                 md.getData().getPoints().size();
         }
 
         if (totalDataPoints <= maxBatchSize) {
-            return delegate.export(metrics);
+            return delegate.export(snapshotted);
         }
 
         List<List<MetricData>> batches =
-            splitIntoBatches(metrics, maxBatchSize);
+            splitIntoBatches(snapshotted, maxBatchSize);
 
         LOGGER.debug(
             "Splitting metrics export: "
@@ -184,6 +189,51 @@ private static void logFailedBatch(
             batchIndex, names);
     }
 
+    /**
+     * Creates defensive snapshots of all MetricData by
+     * copying their data point collections into new
+     * ArrayLists. This prevents
+     * {@link ArrayIndexOutOfBoundsException} in the OTel
+     * SDK marshaling code when callback threads
+     * concurrently modify point collections during export.
+     *
+     * @param metrics the original metrics collection
+     * @return list of snapshotted MetricData
+     */
+    private static List<MetricData> snapshotAllMetrics(
+        final Collection<MetricData> metrics) {
+        List<MetricData> result =
+            new ArrayList<>(metrics.size());
+        for (MetricData md : metrics) {
+            try {
+                result.add(snapshotMetricData(md));
+            } catch (Exception e) {
+                LOGGER.warn(
+                    "Failed to snapshot MetricData:"
+                        + " {}, using original",
+                    md.getName(), e);
+                result.add(md);
+            }
+        }
+        return result;
+    }
+
+    /**
+     * Creates a snapshot of a single MetricData by copying
+     * its points into a new ArrayList and reconstructing
+     * the MetricData with immutable internal data.
+     *
+     * @param md the original MetricData
+     * @return a new MetricData with snapshotted points
+     */
+    private static MetricData snapshotMetricData(
+        final MetricData md) {
+        List<PointData> points =
+            new ArrayList<>(md.getData().getPoints());
+        return createMetricDataForType(
+            md, md.getType(), points);
+    }
+
     /**
      * Splits metrics into sub-batches by data point count.
      * When a single MetricData has more points than the