feat(easytier): instrument hot-path locks, channels, and functions

Wrap the per-packet locks and channels behind hotpath's drop-in wrappers
() so lock contention and
channel flow become visible when the  feature is on, while staying
zero-cost in default builds via cfg-gated dual imports and the no-op
// macros. Annotate the hottest send/recv,
encrypt/decrypt, and forward functions with .

Coverage: peer_conn/peer_manager/peer_map/peer/peer_session/secure_datagram
locks, mpsc/ring/udp/wireguard/fake_tcp channels, quic connection pool,
relay/foreign send paths, and OSPF route lookup (function-level only; its
parking_lot upgradable guards have no hotpath wrapper).

Debug impls that formatted lock fields are updated to dereference the inner
value, and quic's RwPool switches to a manual Debug that skips the locks.

easytier/src/peers/peer_conn.rs

@@ -11,6 +11,9 @@ use std::{
     },
 };
 
+#[cfg(feature = "hotpath")]
+use hotpath::wrap::tokio::sync::Mutex;
+#[cfg(not(feature = "hotpath"))]
 use tokio::sync::Mutex;
 
 use base64::Engine as _;
@@ -381,12 +384,12 @@ impl PeerConn {
             session_filter,
             noise_handshake_result: None,
 
-            tunnel: Arc::new(Mutex::new(
+            tunnel: Arc::new(hotpath::mutex!(tokio::sync::Mutex::new(
                 Box::new(guard!([mut mpsc_tunnel] mpsc_tunnel.close()))
                     as Box<dyn Any + Send + 'static>,
-            )),
+            ))),
             sink,
-            recv: Mutex::new(Some(recv)),
+            recv: hotpath::mutex!(tokio::sync::Mutex::new(Some(recv))),
             tunnel_info,
 
             tasks: JoinSet::new(),
@@ -1463,6 +1466,7 @@ impl PeerConn {
         });
     }
 
+    #[cfg_attr(feature = "hotpath", hotpath::measure(impl_type = "PeerConn"))]
     pub async fn send_msg(&self, msg: ZCPacket) -> Result<(), Error> {
         Ok(self.sink.send(msg).await?)
     }