Add update class method to DataUpdateCoordinator

[frenck]

Proposed change

This PR implements an update method (async_update_data) in the DataUpdateCoordinator class.

This allows one to extend the DataUpdateCoordinator and implement an override on the update method.

As suggested by @balloob @ #32565 (comment)

Will be used to cleaning up the implementation of PR #32565

PS: Added one additional test, out of the scope of this PR, to improve coverage.

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 #
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Checklist

• The code change is tested and works locally.
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• 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 and included derived files by running: python3 -m script.hassfest.
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