WIP: Set HA device class "voltage" for voltage entries

[codecov[bot]]

Codecov Report

Base: 64.56% // Head: 64.74% // Increases project coverage by +0.18% :tada:

Coverage data is based on head (ea1ae78) compared to base (7b650f9). Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #28 +/- ## ========================================== + Coverage 64.56% 64.74% +0.18% ========================================== Files 21 21 Lines 776 780 +4 ========================================== + Hits 501 505 +4 Misses 275 275 ``` | [Impacted Files](https://codecov.io/gh/jedie/pysmartmeter/pull/28?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jens+Diemer) | Coverage Δ | | |---|---|---| | [pysmartmeter/data\_classes.py](https://codecov.io/gh/jedie/pysmartmeter/pull/28?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jens+Diemer#diff-cHlzbWFydG1ldGVyL2RhdGFfY2xhc3Nlcy5weQ==) | `100.00% <100.00%> (ø)` | | | [pysmartmeter/homeassistant.py](https://codecov.io/gh/jedie/pysmartmeter/pull/28?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jens+Diemer#diff-cHlzbWFydG1ldGVyL2hvbWVhc3Npc3RhbnQucHk=) | `92.98% <100.00%> (+0.12%)` | :arrow_up: | | [pysmartmeter/obis\_map.py](https://codecov.io/gh/jedie/pysmartmeter/pull/28?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jens+Diemer#diff-cHlzbWFydG1ldGVyL29iaXNfbWFwLnB5) | `100.00% <100.00%> (ø)` | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jens+Diemer). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jens+Diemer)

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