Dahua VTO custom integration

Thanks for creating this integration. I was able to get it working without too much effort.

Just to confirm, it looks like this integration polls the VTO to learn about state changes (e.g. doorbell button), and it's not an asynchronous solution, correct?

Background is that I am considering the MQTT path because it appears to be truly async, but there's a bit more to that including running a docker container...