refactor: replace std::sync::mpsc with flume for improved channel performance

Migrate internal message passing to flume to leverage better performance and additional features like eventual fairness and selection.

src/metrics.rs

@@ -1,13 +1,13 @@
 use crate::Config;
 use crate::config::{MeasurementType, ObservabilityProtocol};
 use crate::time::Time;
+use flume::{Receiver, RecvTimeoutError, Sender};
 use log::{error, info, warn};
 use rustix::time::ClockId;
 use std::fmt::Write;
 use std::net::{IpAddr, TcpStream, UdpSocket};
 use std::sync::Arc;
 use std::sync::atomic::{AtomicU32, Ordering};
-use std::sync::mpsc::{Receiver, RecvTimeoutError, SyncSender};
 use std::time::Duration;
 
 const MAX_RECONNECT_BACKOFF: u64 = 60;
@@ -122,12 +122,12 @@ pub enum Metric {
 
 #[derive(Clone)]
 pub struct MetricsSender {
-    tx: Option<SyncSender<(Metric, u64)>>,
+    tx: Option<Sender<(Metric, u64)>>,
     dropped: Arc<AtomicU32>,
 }
 
 impl MetricsSender {
-    pub fn new(tx: SyncSender<(Metric, u64)>, dropped: Arc<AtomicU32>) -> Self {
+    pub fn new(tx: Sender<(Metric, u64)>, dropped: Arc<AtomicU32>) -> Self {
         Self {
             tx: Some(tx),
             dropped,