Merge Zone into Circuit if there is only one Zone in a Circuit

[ml1nk]

Before submitting a new issue

• [x] I'm not using the older Vaillant sensoAPP (which is unsupported by this integration)
• [x] I redownloaded the latest release and restarted Home Assistant
• [x] I've enabled debug logs and attached the relevant logs to this ticket

Problem description

Currently there is a device for every Zone and every Circuit. Only the Zone is named, but at least in my case there is only one Zone per Circuit. I would like to change the names and device identifier appropriately, so that there is just one Device for every combination. If another Zone is added to a circuit this should resolve nicely, as the unique ids are unchanged but the names are updates correctly.

@signalkraft I would like create a pull request i the coming days, if you agree with the proposed changes. It think, this should be an easy change.