feat: implement cross-node event broadcasting with NATSEventBus

- Add UpdateVersionCache method to JetStreamEventStore for cache synchronization
- Add SubscribeToEventStored convenience helper to NATSEventBus
- Create integration tests for cross-node broadcasting scenarios
- Add example demonstrating NATSEventBus + JetStreamEventStore integration

store/helpers_test.go

@@ -0,0 +1,36 @@
+//go:build integration
+// +build integration
+
+package store
+
+import (
+	"testing"
+
+	"github.com/nats-io/nats.go"
+)
+
+// getTestNATSConnection returns a NATS connection for testing.
+// This helper is used by benchmark tests that require NATS.
+func getTestNATSConnection(t *testing.T) *nats.Conn {
+	nc, err := nats.Connect(nats.DefaultURL)
+	if err != nil {
+		t.Skipf("NATS not available: %v", err)
+	}
+	return nc
+}
+
+// getVersionFromEvent extracts version from EventStored event data.
+func getVersionFromEvent(data map[string]interface{}) int64 {
+	switch v := data["version"].(type) {
+	case float64:
+		return int64(v)
+	case int64:
+		return v
+	case int:
+		return int64(v)
+	case uint64:
+		return int64(v)
+	default:
+		return 0
+	}
+}