[extractor/twitter:spaces] Add scheduled time (release_timestamp) for live spaces

[CeruleanSky]

Description of your pull request and other information

Add scheduled start time for spaces

Template

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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
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Copilot Summary

🤖 Generated by Copilot at bb3b3b1

Summary

🕒🔊🐦

Add support for extracting release timestamps from Twitter Spaces audio streams. Use the release_timestamp field in yt_dlp/extractor/twitter.py to store the scheduled start time of the stream.

Oh we're the coders of the Twitter Spaces
We stream the audio from many places
We add release_timestamp to the streams
To schedule them ahead, so we can dream

Walkthrough

• Extract the scheduled start time of Twitter Spaces audio streams and convert it to Unix timestamp (link)
• Add the extracted start time as release_timestamp field to the info dictionary of the audio streams (link)

[pukkandan]

Add/update test

[pukkandan]

• At least skimmed through contributing guidelines including yt-dlp coding conventions

Next time, pls actually follow this