Make extended attribute writing more robust against filesystem limits.

[eric321]

IMPORTANT: PRs without the template will be CLOSED

Description of your pull request and other information

Some filesystems limit the size of extended attributes (e.g., 4kB on ext4). The description can easily get close to or exceed this. By writing it last, we avoid missing out on the other ones.

Also catch each write_xattr() failure individually, so we can report which attributes were not written.

Template

Before submitting a pull request make sure you have:

• At least skimmed through contributing guidelines including yt-dlp coding conventions
• Searched the bugtracker for similar pull requests

In order to be accepted and merged into yt-dlp each piece of code must be in public domain or released under Unlicense. Check all of the following options that apply:

• I am the original author of this code and I am willing to release it under Unlicense
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What is the purpose of your pull request?

• Fix or improvement to an extractor (Make sure to add/update tests)
• New extractor (Piracy websites will not be accepted)
• Core bug fix/improvement
• New feature (It is strongly recommended to open an issue first)

[Grub4K]

No reason to change it to a list, dicts are ordered

[eric321]

done

[Grub4K]

Try to avoid force pushing, prs will be squashed on merge, so take as many commits as you want