fix: revoke Blob URLs created by p5.File

[slash-init]

Resolves #9134

Changes:

• Track Blob URLs created by p5.File._load() on the owning p5 instance.
• Automatically revoke all tracked Blob URLs when p5.remove() is called.
• Add p5.File.revoke() for explicitly releasing a file's Blob URL.
• Make p5.File.revoke() idempotent and remove revoked URLs from the instance's tracking set.
• Pass the p5 instance through both createFileInput() and Element.drop() so media files are tracked correctly.
• Add unit tests covering Blob URL tracking, automatic cleanup, manual revocation, and both file-loading entry points.

PR Checklist

• npm run lint passes
• [Inline reference] is included / updated
• Unit tests are included / updated

[rk-3001]

Hi, I'd like to take this on.
Cause: p5.File._load() creates blob URLs for audio/video files via URL.createObjectURL() but never revokes them, so they leak for the page's lifetime instead of the sketch's.
Fix: track created URLs in a _blobUrls Set on the p5 instance (passed through from createFileInput/drop), revoke + clear them in p5.remove(), and add a file.revoke() method for early manual cleanup. I'll include unit tests.
I can work on this...