Add route update metrics tracking to PrefixHandler

- Add RecordIPv4Update and RecordIPv6Update to metrics package
- Add SetMetricsTracker method to PrefixHandler
- Track IPv4/IPv6 route updates when processing announcements
- Add GetMetricsTracker method to Streamer to expose metrics

internal/streamer/streamer.go

@@ -195,6 +195,11 @@ func (s *Streamer) GetMetrics() metrics.StreamMetrics {
 	return s.metrics.GetStreamMetrics()
 }
 
+// GetMetricsTracker returns the metrics tracker instance
+func (s *Streamer) GetMetricsTracker() *metrics.Tracker {
+	return s.metrics
+}
+
 // HandlerStats represents metrics for a single handler
 type HandlerStats struct {
 	Name           string