* Add unique id's to Vallox entities
* Cache uuid properties
Requested in code review.
Caching None isn't a problem as the underlying implementation of get_uuid
in the vallox_websocket_api library can never return None.
* Simplify get_uuid type check
Based on review comments.
* Set _attr_unique_id in init
* Import the library get_uuid under a different name
There are a few options here:
1. Rename the get_uuid method with a synonym
2. Import get_uuid under a different name
3. Convert get_uuid into a property
4. Rename get_uuid in the Vallox library
None of these options is that appealing. I'll start with option two,
anyways.
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