Quic client stats (#24195)

* Add metrics to connection-cache to measure cache hits and misses

* Add congestion stats

* Add more client stats

* Review comments

Co-authored-by: Ryan Leung <ryan.leung@solana.com>

metrics/src/lib.rs

@@ -4,7 +4,28 @@ pub mod datapoint;
 mod metrics;
 pub mod poh_timing_point;
 pub use crate::metrics::{flush, query, set_host_id, set_panic_hook, submit};
-use std::sync::Arc;
+use std::sync::{
+    atomic::{AtomicU64, Ordering},
+    Arc,
+};
+
+// To track an external counter which cannot be reset and is always increasing
+#[derive(Default)]
+pub struct MovingStat {
+    value: AtomicU64,
+}
+
+impl MovingStat {
+    pub fn update_stat(&self, old_value: &MovingStat, new_value: u64) {
+        let old = old_value.value.swap(new_value, Ordering::Acquire);
+        self.value
+            .fetch_add(new_value.saturating_sub(old), Ordering::Release);
+    }
+
+    pub fn load_and_reset(&self) -> u64 {
+        self.value.swap(0, Ordering::Acquire)
+    }
+}
 
 /// A helper that sends the count of created tokens as a datapoint.
 #[allow(clippy::redundant_allocation)]