[youtube] fix chapters extractor (fix #24819)

[jaimebl]

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Description of your pull request and other information

That's a fix for issue #24819

It modifies the regular expression to capture chapters from description when they follow this pattern:
pattern: 00:00 - 09:24 <title>

You can see an example of that here:
https://www.youtube.com/watch?v=gBRKnvK1JUE

[dstftw]

For this pattern you must extract start and end time from each entry.

[anabis]

Hello, there is another way to get the chapters names and timestamp without hazardously parsing the description, it is now in an inline JSON in the page, I don't know Python but I you can get the info like so :
curl -s "https://www.youtube.com/watch?v=AK9r27jWVrc" | grep "ytInitialData" | grep -o "{.*}" | jq '.playerOverlays.playerOverlayRenderer.decoratedPlayerBarRenderer.decoratedPlayerBarRenderer.playerBar.chapteredPlayerBarRenderer.chapters'

[someziggyman]

Looks like this solution fixes cases for timecodes formatted like this: "00:12 some title of the chapter"
However, it fails for timecode formats like this one video: https://www.youtube.com/watch?v=Le0-eaxQ1_k

And these are mystery, but for some reason timecodes are null as well:
https://www.youtube.com/watch?v=YhO_E8xm0aY
https://www.youtube.com/watch?v=7wriyeBB5hY

I guess it's some regex problem and it may be rather complicated to cover all the formatting cases, however decided t post this comment here. Thank you for making youtube-dl better!