Import util.dt as dt_util in remaining tests, enforce with ruff

[scop]

Proposed change

Datetime related module names are unfortunate, but being consistent with how they're imported helps. The whole components tree has been made to import homeassistant.util.dt as dt_util, this PR contains the remaining changes in other parts of the tree, and makes ruff enforce the naming.

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)
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Additional information

• This PR fixes or closes issue: fixes #
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[frenck]

Nice, thanks @scop 👍

../Frenck

[scop]

Cheers, thanks for the quick reviews 👍

[frenck]

Some test failures remain, could you take a look?

../Frenck

[home-assistant]

Please take a look at the requested changes, and use the Ready for review button when you are done, thanks 👍

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