feat: add pause-by-duration control for SlidevVideo

[Jeffrey0117]

This PR adds support for pause=[1,2,3,'end'] format in SlidevVideo component.

The video now plays segment-by-segment with user click between segments. Supports fractional seconds like [3.5, 2.5, 3] Ends with autoplay or manually controlled 'end' keyword.

Fixes #2177 - Clickable Video

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[Jeffrey0117]

Hi, I've added support for segmented video playback with the pause=[1,2,3,'end'] format. This addresses #2177 and allows better interactivity with videos in slides. Tested with fractional durations and multiple use cases. Let me know if anything needs adjustment!

[Jeffrey0117]

Hi, I’ve updated the PR — reverted the README changes and added a new English docs page for the video playback demo.
Please let me know if there’s anything else I should adjust. Thanks a lot for your guidance!