Update VariantProp type merging logic for Compose interface

[lunelson]

Description

This PR primarily addresses the following issue, updating the variant prop merging logic that is applied by the Compose interface, so that the union of available variant prop names is correct.

#256

There are also some secondary simplifications of types, and application of unknown in place of any.

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

Before submitting the PR, please make sure you do the following

• Read the Contributing Guidelines.
• Follow the Style Guide.
• Check that there isn't already a PR that solves the problem the same way to avoid creating a duplicate.
• Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. fixes #123).

[vercel]

@lunelson is attempting to deploy a commit to the cva Team on Vercel.

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[joe-bell]

Thanks @lunelson! Bit stretched for time at the moment but I'll try to get around to testing this. Really appreciate the contribution 🙏

[joe-bell]

Any reason for adding the export?

[lunelson]

Hey @joe-bell thanks for the quick review, and sorry for the slow response, I was on the road after I submitted this, until today.

I must have added this when I was tinkering around, in order to use this type in a scratch test file; I'll remove it.

I also realized after the fact that I could possibly add some type-testing coverage, since you have vitest set up here; and that I hadn't written my commit message with the conventional format. Thoughts?