Migrate binary sensor device classes to StrEnum

[frenck]

Breaking change

This PR deprecates the use of the DEVICE_CLASS_* constants and DEVICE_CLASSES constant for binary_sensor entities. Use the BinarySensorDeviceClass enum instead.

Proposed change

Replaces the device class constants of the binary sensor platform with a StrEnum.

The old CONST is currently still accepted and working (backward compatible). This gives core and custom integration time to adjust.

At this point, I've not set a deprecation period as it is hard to indicate how long this would take.

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
• New feature (which adds functionality to an existing integration)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

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• This PR fixes or closes issue: fixes #
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[balloob]

I don't know this integration, is this correct?

[frenck]

Previously it used a hard coded string in its parent class to "power" for all iets platforms...

So this makes it specific on this platform to fix that (and make mypy happy as it now has catches this bug)