Fix current_cover_tilt_position for shades, add base class

[TheJulianJES]

Proposed change

This PR fixes an issue where the current_cover_tilt_position property was removed for the Shade implementation, based on the LevelControl cluster (in #376).

The Home Assistant integration does not differentiate between our Cover and Shade implementation, so tries to access the current_cover_tilt_position attribute/property regardless: https://github.com/home-assistant/core/blob/d23c9f715e1f7772ec8ae176f3db4b9afa7db95d/homeassistant/components/zha/cover.py#L122-L125

We need to make sure we provide it in all our cover implementations, so this PR adds it back, returning None by default, as a Shade cannot support tilt.

A new abstract BaseCover class is also added to make sure all relevant methods are implemented by the Cover and Shade implementations.

Additional information

Should address:

• Upgrade to 2025.4.x breaks ZHA shade home-assistant/core#142815
• Keen smart vents no longer can be controlled after core update to 2025.4.1 home-assistant/core#142601

We should likely add tests for this in HA in the future. I'm guessing Shade is not covered at all.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.69%. Comparing base (2e8fbe8) to head (2195961).
Report is 1 commits behind head on dev.

Additional details and impacted files

@@           Coverage Diff           @@
##              dev     #416   +/-   ##
=======================================
  Coverage   96.68%   96.69%           
=======================================
  Files          61       61           
  Lines        9834     9863   +29     
=======================================
+ Hits         9508     9537   +29     
  Misses        326      326           

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[puddly]

Could we derive both of them from a single abstract base class that implements the proper API?

[TheJulianJES]

The added line is uncovered, but it looks like all ZHA tests generally use the state property to access various state of the entities. But we do not include the tilt percentage in the state for shades, as it's always None, so we'll need to access that property directly in tests, should be fine though.
-> Added in 2195961 (#416)

Compared to accessing the state via state in ours tests, HA directly accesses the different properties.

[TheJulianJES]

Could we derive both of them from a single abstract base class that implements the proper API?

Probably.

[TheJulianJES]

The implementations don't share a lot, so the commit is really only the shared API used by HA and setting PLATFORM + _attr_primary_weight.
Also, it seems like ruff doesn't enforce whether to have pass or just the docstring in empty methods. What do we prefer for that? (edit: I guess nothing, so Codecov doesn't complain)

async_open_cover_tilt, async_close_cover_tilt, async_set_cover_tilt_position, and async_stop_cover_tilt are methods only used by Cover from HA. I've not added these to the base class, as we'd also need to implement them for Shade otherwise, and HA should only call them if the supported_features contain the corresponding tilt features.

(On an unrelated note, we should not really set _attr_translation_key if a device class is already present, as the generic device class names should be fine for our purpose and we don't really need another one yet.)