Move to StrEnum with backport for older Python versions

[iMicknl]

No description provided.

[fetzerch]

This PR causes a change of all sensor unique_id in https://github.com/home-assistant/core/blob/dev/homeassistant/components/overkiz/entity.py#L117C84-L117C84 between 2023.8.4 (with pyoverkiz 1.9.0) and the current dev (with pyoverkiz 1.10.1). This leads to new entity_ids and essentially duplicated and unavailable entities. I'm not sure if that's an intentional breaking change, but I guess it's rather an issue that just slipped in.

The old Enum has __str__ set to {classname}.{optionname} while StrEnum uses {optionvalue}. E.g unique_id="io://XXXX-XXXX-XXXX/XXXXXXX-OverkizState.CORE_DISCRETE_RSSI_LEVEL" became unique_id="io://XXXX-XXXX-XXXX/XXXXXXX-core:DiscreteRSSILevelState" (you can double check that in .storage/core.entity_registry).

In order to change it back to the old behavior we can either change the integration to use self.entity_description.key.__class__.__name__.self.entity_description.key.name in https://github.com/home-assistant/core/blob/dev/homeassistant/components/overkiz/entity.py#L117C84-L117C84 or override __str__ in the library. I'm not sure if there's any other place that relied on the old behavior but if not it's probably easiest to adapt the integration.

I have not found a corresponding issue in the integration yet. I did find home-assistant/core#99404, but I'm not sure if it's the same.