chore: migrate button components

[mdeliatf]

Description

Migrates Button, IconButton, and ButtonSwitch from Stitches to vanilla-extract with full feature parity.

Fixes https://github.com/traefik/hub-issues/issues/2390

Preview

No visual changes.

Breaking changes

None.

How to test?

Run yarn storybook and verify Comparison stories for all 3 components.

Good PR checkboxes

• Change has been tested
• Added/Updated tests
• Added/Updated stories
• PR follows conventions
• Labels are set
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Good Review checkboxes

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- [ ] I've tested the changes
- [ ] I've agreed on the unit tests (soon to come)
- [ ] I've checked the stories
- [ ] I've read the code and understood it
- [ ] I don't have any more questions
- [ ] I've described any optional improvements
- [ ] I checked PR follows [conventions](https://github.com/traefik/faency#how-to-contribute)

[traefiker]

🎉 This PR is included in version 12.0.7 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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