Fix lint issues

mtglib/internal/relay/relay.go

 	defer func() {
 		syncer.Flush()
 		releaseSyncPair(syncer)
-		src.CloseRead()
-		dst.CloseWrite()
+		src.CloseRead()  // nolint: errcheck
+		dst.CloseWrite() // nolint: errcheck
 		wg.Done()
 	}()
 

mtglib/internal/relay/sync_pair.go

 	s.mutex.Lock()
 	defer s.mutex.Unlock()
 
-	n, err := s.writer.Write(p) // nolint: wrapcheck
+	n, err := s.writer.Write(p)
 
 	// optimization for a case when we have a small package and want to avoid a
 	// delay in readTimeout. In that case, we assume that peer has finished to
 		err = s.writer.Flush()
 	}
 
-	return n, err
+	return n, err // nolint: wrapcheck
 }
 
 func (s *syncPair) Flush() error {