Use common entity class

[CFenner]

Uses a common entity class to reuse code for _attr_device_info and other common attributes like _attr_has_entity_name, _attr_unique_id, ent, ...

• real world test

[astrandb]

Thanks a lot for this work. I have had this clean-up on my own to-do list for a long time but never did anything about it.
I will do some verification and testing and then it should be ready to merge.