feat: add Embla initialization hooks

[sunmorgn]

Summary

Adds stable JavaScript hooks around rtCarousel's Embla initialization so projects can adjust Embla options, append Embla plugins, and access the initialized Embla API for methods and events without forking the plugin.

Type of change

• Bug fix
• New feature
• Enhancement/refactor
• Documentation update
• Test update
• Build/CI/tooling

Related issue(s)

Closes #144

What changed

• Added rtcamp.carouselKit.emblaOptions to filter the options passed to EmblaCarousel.
• Added rtcamp.carouselKit.emblaPlugins to filter the Embla plugin array after the built-in Autoplay plugin is configured.
• Added rtcamp.carouselKit.emblaInit so integrations can call Embla methods or subscribe to Embla events after initialization.
• Added API documentation and unit test coverage for the extension hooks.

Breaking changes

Does this introduce a breaking change? If yes, describe the impact and migration path below.

• Yes — migration path:
• No

Testing

Describe how this was tested.

• Unit tests
• Manual testing - tested numerous previously unavailable options and all official and up-to-date third-party plugins.
• Cross-browser testing (if UI changes)

Test details:

• npm run lint:js
• npm run lint:js:types
• npm run test:js -- --runTestsByPath src/blocks/carousel/__tests__/view.test.ts
• npm run build
• Manually tested in a local WordPress install by adding site-level filters/actions for Embla options, plugins, methods, and events, including Auto Height, Auto Scroll, Class Names, Fade, Wheel Gestures, and A11y.

Screenshots / recordings

Not applicable; this change exposes developer extension hooks and does not alter saved markup or default carousel behavior.

Checklist

• I have self-reviewed this PR
• I have added/updated tests where needed
• I have updated docs where needed
• I have checked for breaking changes

[sunmorgn]

Additional local manual test after adding rtcamp.carouselKit.emblaInit:

• Updated a local WordPress test install to use the PR build.
• Registered a site-level addAction( "rtcamp.carouselKit.emblaInit", ... ) listener from the active theme.
• Confirmed the action fired for 15 carousel initializations on a page containing multiple carousel variants.
• Confirmed the callback receives the Embla API instance plus the expected context object, and can call methods such as selectedScrollSnap(), canScrollPrev(), and canScrollNext().
• No browser console errors were reported during the test.

[sunmorgn]

Additional local test using WordPress block-style classes:

• Switched the local theme integration from temporary has-embla-* classes to is-style-* block style classes.
• Confirmed is-style-auto-height triggers the theme-level rtcamp.carouselKit.emblaPlugins filter and loads the autoHeight Embla plugin.
• Confirmed the Auto Height carousel container updates height between slides (201px to 267px) after navigation.
• Confirmed no old has-embla-* classes remain on the test page and no browser console errors were reported.

This keeps the PR API compatible with normal WordPress block style workflows.