[SpankBang] Improve extractors

[dirkf]

Boilerplate: mixed code, improvement

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• Searched the bugtracker for similar pull requests
• Read adding new extractor tutorial
• Read youtube-dl coding conventions and adjusted the code to meet them
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What is the purpose of your pull request?

• Bug fix
• Improvement
• New extractor
• New feature

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Description of your pull request and other information

This PR updates the SpankBang extractor module. The main changes are:

• SpankBangIE back-ported from yt-dlp (small changes)
• SpankBangPlaylistIE reworked to support multi-page playlists.

Resolves #30728.

[afterdelight]

could you add channel page support?

[afterdelight]

thanks!

[dirkf]

See yt-dlp/yt-dlp#5156 (comment).