[broadcast] use subscribe metric and batch increment

broadcast/src/buffered/engine.rs

@@ -447,8 +447,10 @@ impl<E: Clock + Spawner + Metrics, P: PublicKey, M: Committable + Digestible + C
             let dropped_count = initial_len - waiters.len();
 
             // Increment metrics for each dropped waiter
-            for _ in 0..dropped_count {
-                self.metrics.get.inc(Status::Dropped);
+            if dropped_count > 0 {
+                self.metrics
+                    .subscribe
+                    .inc_by(Status::Dropped, dropped_count as u64);
             }
 
             !waiters.is_empty()

broadcast/src/buffered/ingress.rs

@@ -7,7 +7,7 @@ use futures::{
     SinkExt,
 };
 
-/// Message types that can be sent to the `Mailbox`
+/// Message types that can be sent to the [`Mailbox`]
 pub enum Message<P: PublicKey, M: Committable + Digestible> {
     /// Broadcast a [crate::Broadcaster::Message] to the network.
     ///