Fix crash while scrubbing some audio files

[7w1]

Description

I don't think we technically do "scrubbing" but idk any other word for it.

Fixes the crash while scrubbing audio files by pretty much just spamming infinity checks everywhere and adding a helper to calculate duration properly (previously the voice message content never specified duration so it would only appear after the file fully loaded in).

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings

AI disclosure:

• Partially AI assisted (clarify which code was AI assisted and briefly explain what it does).
• Fully AI generated (explain what all the generated code does in moderate detail).

[github-actions]

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Status	Preview URL	Commit	Alias	Updated (UTC)
✅ Deployment successful!	https://pr-902-sable.raspy-dream-bb1d.workers.dev	898d22c	pr-902	Mon, 25 May 2026 02:57:21 GMT