Use websocket fixture in deCONZ light tests

[Kane610]

Breaking change

Proposed change

Depends on #47738
Use new websocket fixture
Localize test fixtures
Improve asserts

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

Example entry for configuration.yaml:

# Example configuration.yaml

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue: Deconz websocket fixture #47738
• Link to documentation pull request:

Checklist

• The code change is tested and works locally.
• Local tests pass. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.
• I have followed the development checklist
• The code has been formatted using Black (black --fast homeassistant tests)
• Tests have been added to verify that the new code works.

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  Updated by running python3 -m script.gen_requirements_all.
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[Kane610]

Thanks @frenck 🎉