Use SyncWrite call to send a packet to proxy

mtglib/internal/doppel/conn_test.go

 
 	go func() {
 		defer close(syncDone)
-		c.SyncWrite([]byte("exclusive"))
+		c.SyncWrite([]byte("exclusive")) //nolint: errcheck
 	}()
 
 	// Give SyncWrite time to acquire the lock.
 
 	go func() {
 		defer close(writeDone)
-		c.Write([]byte("blocked"))
+		c.Write([]byte("blocked")) //nolint: errcheck
 	}()
 
 	// SyncWrite should finish first.

mtglib/proxy.go

 	}
 	defer clientConn.Stop()
 
-	if _, err := clientConn.Write(noise); err != nil {
+	if _, err := clientConn.SyncWrite(noise); err != nil {
 		ctx.logger.InfoError("cannot send the first packet", err)
 		return
 	}