[MWPW-199341] Reduce motion effect when applied not seen working on carousel

[SamSawant876]

Changes:

• Replaced the index-based isSlideVisible() check with getOverlapRatio(), which compares a video's getBoundingClientRect() against the carousel wrapper's clipped (overflow: hidden) bounds.
• Added VISIBILITY_THRESHOLD (0.5) — a slide's video only stays exempt from pausing if at least half of it is still visible in the wrapper, so a hinting layout's partial "peek" of a neighboring slide doesn't count as fully in view.
• checkSlideForVideo() / pauseVideosOutOfView() now run against every slide instead of only the previously-active one, so a video started on a peeking/inactive slide is no longer invisible to the pause check.
• Added waitForSlideTransition() so the visibility check runs once the slide track's transform transition actually settles (with a TRANSITION_FALLBACK_MS timeout as a safety net), guarded to the track's own transform property so a child slide's own opacity transition can't resolve it early.
• Added test coverage for the visibility-ratio thresholds and the boundary-path pause call.

Expected video behaviour:

Reduce motion on: Videos do not auto-play on arrow navigation, user must click play.
User clicks play: Video plays while its slide remains sufficiently visible in the carousel viewport.
User swipes / navigates away (either direction): Video's slide is no longer sufficiently visible and is paused.
Navigation blocked at a disable-circular-nav boundary: A playing video that's actually out of view still gets paused, even though the active slide didn't change.
Slide returns to view: Video stays paused, it does not auto-resume. User must click play again.

Test URLs:

Before: https://main--da-cc--adobecom.aem.live/products/firefly/features/image-to-video
After: https://main--da-cc--adobecom.aem.live/products/firefly/features/image-to-video?milolibs=mwpw-199341-firefly-carousal-fix

Resolves: Resolves: MWPW-199341

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Commits

• 0351638 ✅ (latest)
• 359e822 ✅