feat: implement stale client removal after timeout

- add goroutine to remove stale clients from the connection pool
- update client struct to track `LastPong` time
- set write deadline for websocket connections
- move package variables and const to `vars.go`
- log additional information when broadcasting errors

🤖

cmd/server/main.go

@@ -54,6 +54,7 @@ func Start() {
 	r := http.NewServeMux()
 	r.HandleFunc("/", websocket.HandleConnection)
 	go websocket.SendPermanentBroadCastMessage()
+	go websocket.RemoveStaleClients()
 
 	helper.Logger.Info("GoTomato started", "version", metadata.GoTomatoVersion)
 	helper.Logger.Info("Websocket listening", "address", listen)