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/pinger.rs

@@ -2,12 +2,12 @@ use crate::MeasurementType;
 use crate::SHUTDOWN;
 use crate::metrics::{Metric, MetricsSender};
 use crate::util::RwLockExt;
+use flume::Sender;
 use icmp_socket2::socket::IcmpSocket;
 use icmp_socket2::{IcmpSocket4, Icmpv4Packet};
 use log::{debug, info, warn};
 use std::net::{IpAddr, Ipv4Addr};
 use std::sync::atomic::Ordering;
-use std::sync::mpsc::Sender;
 use std::sync::{Arc, RwLock};
 use std::time::{Duration, Instant};
 use std::{io, thread};