Fix unit parsing in Tuya climate entities

[epenet]

Proposed change

Support for TEMP_UNIT_CONVERT data point was accidentaly removed in #156977

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)
• Deprecation (breaking change to happen in the future)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Additional information

• This PR fixes or closes issue: fixes Tuya error Entity climate.itc_308_wifi_thermostat does not support action climate.set_temperature #157921
• This PR is related to issue:
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[home-assistant]

Hey there @tuya, @zlinoliver, mind taking a look at this pull request as it has been labeled with an integration (tuya) you are listed as a code owner for? Thanks!

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[Copilot]

Pull request overview

This PR fixes a regression where support for the TEMP_UNIT_CONVERT data point was accidentally removed in PR #156977. The fix restores the ability for Tuya climate entities to properly parse and use temperature units from devices that expose a temperature unit conversion setting.

Key changes:

• Restores temperature unit detection logic by reading the TEMP_UNIT_CONVERT dpcode and applying it to temperature wrappers with empty unit fields
• Updates test fixture handling to avoid double JSON encoding when values are already strings
• Adds comprehensive test coverage for a device using TEMP_UNIT_CONVERT functionality

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
homeassistant/components/tuya/climate.py	Adds logic to check for TEMP_UNIT_CONVERT dpcode and populate empty temperature unit fields with the device's current unit setting
tests/components/tuya/conftest.py	Updates device fixture creation to handle pre-stringified JSON values, preventing double encoding
tests/components/tuya/fixtures/wk_B0eP8qYAdpUo4yR9.json	Adds test fixture for ITC-308-WIFI thermostat device with TEMP_UNIT_CONVERT support and empty unit fields
tests/components/tuya/snapshots/test_climate.ambr	Adds expected test snapshots for the new fixture in both metric and US customary unit systems