Define binary_sensor entity attribute as class variables

[frenck]

Proposed change

Defines BinarySensorEntity entity attributes as class variables,
followup of the implementation started in #50925

For full context #50925 is the best place to take a look.

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• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
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• This PR fixes or closes issue: fixes #
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[frenck]

Parent merged, marked ready for review.

[KapJI]

_attr_is_on is not used.

[frenck]

Well spotted, opening a fix for that 👍 (after CI has been fixed)