fix: set sensor device class

[shred86]

Change

• Specify device class for sensors to allow users to specify the unit of measurement for each entity.

Details

• Reverts a previous PR but this still fixes No longer shows in Miles only km #284. Specifically, if a UK user has their Home Assistant Unit System set to metric, they can still set the units for the odometer to miles (one example).

[alandtse]

Please note, it's not just the PR title that should follow the convention. It's the actual commit itself. There are plugins that help enforce this like comittizen. I'm squashing these to fix these for you, but once you figure it out you can just start merging.