[bandlab] add extractor (supersedes #31206) (Closes #31184)

[aiur-adept]

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• Searched the bugtracker for similar pull requests
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• Bug fix
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• New extractor
• New feature

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Description of your pull request and other information

Bandlab extractor for individual posts, albums, and collections

Closes #31184

[aiur-adept]

This is a continuation of #31206

[aiur-adept]

@dirkf I think this can merge now

[dirkf]

You can put (eg) Supersedes, closes #31206 in the PR description to have that PR closed automatically when this is merged.

[seproDev]

Consider taking a look at yt-dlp/yt-dlp#11535
It's for yt-dlp (a fork of youtube-dl), so no Python 2.6 compat, and I am not sure if all the helpers introduced in yt-dlp have made their way to youtube-dl, but it should be a solid reference point for improving this extractor.
I spend a fair bit of time making sure the extractor works with all kinds of links (tracks, revisions, videos, posts, embeds, unlisted tracks, private tracks). The extractor in yt-dlp also extracts more metadata than this current PR.