Add speed conversion function

[rianadon]

Proposed change

Similar to how the distance and temperature units have conversion functions, I created one for converting between speeds, along with tests.

While this refactor does not result in any immediate gains, this function will help implement #48641, which requires converting speeds between user-configurable units.

I've also edited existing kph <--> mph unit conversions using the length conversion function to use the speed conversion function.

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

Additional information

Checklist

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• Local tests pass. Your PR cannot be merged unless tests pass
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• Tests have been added to verify that the new code works.

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[rianadon]

I apologize for the excessive bot pinging, probably due to refactoring across a few different components. I did not expect that to happen.

[github-actions]

There hasn't been any activity on this pull request recently. This pull request has been automatically marked as stale because of that and will be closed if no further activity occurs within 7 days.
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[emontnemery]

This looks mostly good.

One concern though; let's move the adding of a default speed unit for the imperial and metric unit systems to a separate PR:

• SI unit for speed is m/s not km/h, although km/h is probably more commonly used
• The unit traditionally used for wind speed and rainfall may differ from the unit used for other speeds
  • We certainly don't want rainfall in mm/day to be converted to km/h

This can be discussed in a separate PR, then this PR is ready for merge IMO.

[rianadon]

@emontnemery pinging you in case you didn't get notified of my new commits.

I parameterized the tests slightly differently than you suggested (by using only one parameterize call and passing in the expected conversion results). Let me know if you still like your method better.

[emontnemery]

It's OK, I think.
By parametrizing to and from units separately all permutations are tested, but maybe that was a bit over the top.

Just a couple of small comments on the tests.

[rianadon]

I think all of the conversion factors get tested even if there's not every single permutation, since I use every unit at least once.

I don't see your other comments on the tests. Did I accidentally resolve them?

[emontnemery]

I don't see your other comments on the tests. Did I accidentally resolve them?

I forgot to "publish" the review, sorry about that 🤦

[rianadon]

No worries! Thank you for the review. I've addressed the comments.

[emontnemery]

Thanks, @rianadon 👍