perf: do not reset the hearbeat timer on each packet

This behavior was added in [1]. However, there are two problems:

- a new timer is allocated every time a packet is received, which is
wasteful

- the next heartbeat is not actually delayed, since it's the timeout
timer which gets reset, and not the interval timer

Note: delaying the next heartbeat would be a breaking change.

[1]: be7b4e7

lib/socket.ts

@@ -135,19 +135,14 @@ export class Socket extends EventEmitter {
     debug(`received packet ${packet.type}`);
     this.emit("packet", packet);
 
-    // Reset ping timeout on any packet, incoming data is a good sign of
-    // other side's liveness
-    this.resetPingTimeout(
-      this.server.opts.pingInterval + this.server.opts.pingTimeout
-    );
-
     switch (packet.type) {
       case "ping":
         if (this.transport.protocol !== 3) {
           this.onError("invalid heartbeat direction");
           return;
         }
         debug("got ping");
+        this.pingTimeoutTimer.refresh();
         this.sendPacket("pong");
         this.emit("heartbeat");
         break;
@@ -158,6 +153,7 @@ export class Socket extends EventEmitter {
           return;
         }
         debug("got pong");
+        clearTimeout(this.pingTimeoutTimer);
         this.pingIntervalTimer.refresh();
         this.emit("heartbeat");
         break;