feat: rename button styler

[leoafarias]

Description

Renames RemixButtonStyler to ButtonStyler across the package API, generated sources, Fortal artifacts, examples, and documentation.

Keeps RemixButtonStyler as a deprecated compatibility alias throughout the beta releases. The alias will be removed in 1.0.0.

Validation

• fvm dart analyze — passed
• fvm flutter test packages/remix/test --reporter=failures-only — 1,884 tests passed
• fvm flutter test packages/remix/test/components/button/button_styler_compatibility_test.dart — passed

Related Issues

None.

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Checklist

Note: Updating the pubspec.yaml and CHANGELOG.md is not required. These are handled automatically during the release process.

• My PR includes unit or integration tests for all changed/updated/fixed behaviors.
• I have updated or added relevant documentation (doc comments with ///).
• I am prepared to follow up on review comments in a timely manner.

Breaking Change

Does this PR require users of the package to manually update their code?

• Yes, this is a breaking change.
• No, this is not a breaking change.