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/settings/validation.rs

@@ -3,6 +3,8 @@
 // SPDX-License-Identifier: MPL-2.0
 //
 
+use crate::settings::ReflectorSettings;
+
 use super::{AdvancedSettings, NetworkSettings, ObservabilitySettings, OutputSettings, Settings};
 use std::error::Error;
 use std::fmt::{self, Display, Formatter};
@@ -88,6 +90,7 @@ impl Settings {
         let mut report = ValidationReport::default();
 
         self.network.validate(&mut report);
+        self.reflectors.validate(&mut report);
         self.output.validate(&mut report);
         self.observability.validate(&mut report);
         self.advanced_settings.validate(&mut report);
@@ -192,6 +195,45 @@ impl NetworkSettings {
     }
 }
 
+impl ReflectorSettings {
+    fn validate(&self, report: &mut ValidationReport) {
+        if self.num_reflectors == 0 {
+            report.error("reflectors.num_reflectors", "must be greater than 0");
+        }
+
+        if self.peer_reselection_time == 0 {
+            report.error("reflectors.peer_reselection_time", "must be greater than 0");
+        }
+
+        if self.files.is_empty() && self.entries.is_empty() {
+            report.error(
+                "reflectors",
+                "at least one reflector file or inline entry is required",
+            );
+        }
+
+        for (index, file) in self.files.iter().enumerate() {
+            if file.trim().is_empty() {
+                report.error(
+                    "reflectors.files",
+                    format!("entry {index} must not be empty"),
+                );
+            }
+        }
+
+        for (index, country) in self.countries.iter().enumerate() {
+            if country.len() != 2 || !country.bytes().all(|c| c.is_ascii_alphabetic()) {
+                report.error(
+                    "reflectors.countries",
+                    format!(
+                        "entry {index} ({country:?}) must be an ISO 3166-1 alpha-2 country code"
+                    ),
+                );
+            }
+        }
+    }
+}
+
 impl OutputSettings {
     fn validate(&self, report: &mut ValidationReport) {
         if self.suppress_statistics {
@@ -298,24 +340,6 @@ impl AdvancedSettings {
             self.tick_interval,
         );
 
-        if self.num_reflectors < 5 {
-            report.error(
-                "advanced_settings.num_reflectors",
-                format!("must be at least 5, got {}", self.num_reflectors,),
-            );
-        }
-
-        if self.peer_reselection_time == 0 {
-            report.error(
-                "advanced_settings.peer_reselection_time",
-                "must be greater than 0",
-            );
-        }
-
-        if self.reflector_list_file.trim().is_empty() {
-            report.error("advanced_settings.reflector_list_file", "must not be empty");
-        }
-
         if self.speed_hist_size == 0 {
             report.error(
                 "advanced_settings.speed_hist_size",