feat(measurement): add configurable IRTT reflector measurements

Support optional IRTT measurements alongside ICMP with CSV and inline reflector definitions, repeated UCI registration, authentication, and endpoint-specific stream tracking.

Keep the managed driver running during target acknowledgements and stop and join it on event-loop exits. Carry stream identity through baselines, selection, and rate control so endpoints sharing an IP remain distinct.

src/measurement/model.rs

@@ -20,7 +20,7 @@ pub enum MeasurementSource {
 impl Display for MeasurementSource {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self {
-            MeasurementSource::IcmpEcho => write!(f, "icmp"),
+            MeasurementSource::IcmpEcho => write!(f, "icmp-echo"),
             MeasurementSource::IcmpTimestamp => write!(f, "icmp-timestamps"),
             MeasurementSource::Irtt => write!(f, "irtt"),
             MeasurementSource::TcpSeqAck => write!(f, "tcp-seqack"),