[JioSaavn] Add extractor

[awalgarg]

Description of your pull request and other information

JioSaavn is a large streaming service primarily serving Indian music.

Original PR in youtube-dl: ytdl-org/youtube-dl#20870, unfortunately it wasn't merged back then. I've been maintaining it in my personal fork since and it works well.

Template

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• At least skimmed through contributing guidelines including yt-dlp coding conventions
• Searched the bugtracker for similar pull requests
• Checked the code with flake8 and ran relevant tests

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What is the purpose of your pull request?

• New extractor (Piracy websites will not be accepted)

Copilot Summary

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Summary

🎵🇮🇳🆕

Add support for JioSaavn streaming service. Add jiosaavn.py module with extractors for songs and albums. Import these extractors in _extractors.py.

yt-dlp expands
JioSaavn songs and albums
now in autumn breeze

Walkthrough

• Add support for JioSaavn streaming service (link, link)

• Import JioSaavnSongIE and JioSaavnAlbumIE classes from jiosaavn.py module in _extractors.py (link)
• Define JioSaavnBaseInfoExtractor class to extract initial JSON data from webpage (link)
• Define JioSaavnSongIE class to extract information and media URL of a single song (link)
• Define JioSaavnAlbumIE class to extract information and URLs of all songs in an album (link)
• Add tests and documentation for the new classes (link)

[awalgarg]

Thanks for fixing it up and merging! I've been traveling so couldn't take a look earlier.