feat: edit files from a Gist url

[crivaronicolini]

📝 Summary

Adds support for editing files from a Github Gist url. Closes #5950.

🔍 Description of Changes

There are two ways to enter a Gist url:

1. Direct Raw URLs (gist.github.com/user/gist_id/raw/file_id/filename): We fetch them directly.
2. Standard Gist URLs (gist.github.com/user/gist_id): For these, we make a request to the GitHub Gist API (api.github.com/gists/gist_id) to retrieve metadata. Then we parse the response to find the raw URL of the first Python or Markdown file in the gist.

The code is organized like the Github url flow, with the exception that the extension check is not in the can_read function but in the read function.

📋 Checklist

• I have read the contributor guidelines.
• For large changes, or changes that affect the public API: this change was discussed or approved through an issue, on Discord, or the community discussions (Please provide a link if applicable).
• I have added tests for the changes made.
• I have run the code and verified that it works as expected.

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Project	Deployment	Preview	Comments	Updated (UTC)
marimo-docs	Ready	Preview	Comment	Sep 27, 2025 9:52pm

[github-actions]

All contributors have signed the CLA ✍️ ✅
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[crivaronicolini]

I have read the CLA Document and I hereby sign the CLA

[mscolnick]

thank you for the contribution!

[manzt]

woo! thank you