Fix BEGA color temp channel unsupported check

[TheJulianJES]

Proposed change

This fixes an issue where the "Color temperature channel" select entity for BEGA lights was created, even if the light driver only supports one color temperature channel. On truly "dimmable only" lights with one driver channel only, one attribute still has the correct color temperature (e.g. 3000K), with the other one being set to 0xFFFF.

To fix this, we just do not create the select entity if either driver channel's color temperature is 0xFFFF.

Additional information

Follow-up to:

• Add BEGA light color temperature channel #721

To note again: These lights are not tunable color temperature lights. They can only be fixed to either 3000K or 4000K (depends on exact model). So, this cannot be represented in the Home Assistant light entity model and an extra select entity is needed to switch the driver channel. See the above PR for more notes on this.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.63%. Comparing base (696ab1c) to head (bae74e8).
⚠️ Report is 4 commits behind head on dev.

Additional details and impacted files

@@           Coverage Diff           @@
##              dev     #737   +/-   ##
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  Coverage   97.63%   97.63%           
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  Files          62       62           
  Lines       10814    10814           
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  Hits        10558    10558           
  Misses        256      256           

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[Copilot]

Pull request overview

This PR fixes BEGA “Color temperature channel” select entity creation by treating the feature as unsupported when either of the two reported switchable color temperature attributes is 0xFFFF, preventing the select entity from being created on single-channel (“dimmable only”) BEGA lights.

Changes:

• Update BEGA select entity support check to skip entity creation when switchable_color_temperature_1 or _2 equals 0xFFFF.
• Adjust debug log message to match the new condition.
• Expand test coverage to ensure the select entity is not created when either (or both) temp attributes are 0xFFFF.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
zha/application/platforms/select.py	Fixes _is_supported() logic for BEGA color temp channel select creation.
tests/test_select.py	Adds parametrized test cases covering partial-unsupported (0xFFFF) scenarios.

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[TheJulianJES]

Note: Almost all BEGA lights are named "Smart Dimmable Light". Some of those are only dimmable, others support two color temperature channels. For the latter ones only, the select entity should be created.

I've not added a second diagnostics file for now, since it's kind of hard to distinguish them. Other than the two color temperature channel attributes, only the product_code attribute would differ when read.

I think this test covers it well enough by just updating the attribute (cache), before joining the device.
Side note: It would be nice to have a better way to populate the attribute cache when read for zigpy_device_from_json.