[ie/youtube] Check newly uploaded iOS HLS formats

[bashonly]

Force --check-formats for newly uploaded iOS HLS formats. Adds private __needs_testing format field.

Closes #7747

Template

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Copilot Summary

🤖 Generated by Copilot at 3f66ed9

Summary

🆕📆📺

Add a flag to mark and test potentially problematic HLS formats for newly uploaded YouTube videos. Modify yt_dlp/extractor/youtube.py and yt_dlp/YoutubeDL.py to implement this feature.

YoutubeIE checks
HLS formats for new videos
Winter of glitches

Walkthrough

• Add a flag to mark potentially problematic HLS formats for newly uploaded YouTube videos (link)
• Test and filter out formats that have the flag set in the _check_formats function (link)

[Grub4K]

Not a huge fan of datetime_from_str but its a lot more readable tbh