Make proxyconn channel response async

hub/proxy_conn.go

 const (
 	proxyConnWriteTimeout = 2 * time.Minute
 	proxyConnReadTimeout  = 2 * time.Minute
+
+	proxyConnBackpressureAfter = 10
 )
 
 type ProxyConn struct {
 
 func newProxyConn(req *protocol.TelegramRequest, channelClosed chan<- conntypes.ConnID) *ProxyConn {
 	return &ProxyConn{
-		channelResponse: make(chan *rpc.ProxyResponse),
+		channelResponse: make(chan *rpc.ProxyResponse, proxyConnBackpressureAfter),
 		channelDone:     make(chan struct{}),
 		channelClosed:   channelClosed,
 		req:             req,