异步转Mono

return Mono.create(sink -> rtmClient.subscribe(channelName, options, new ResultCallback<Void>() {
    @Override
    public void onSuccess(Void unused) {
        sink.success(unused);
    }

    @Override
    public void onFailure(ErrorInfo errorInfo) {
        sink.error(new IllegalStateException(errorInfo.getErrorReason()));
    }
}));