fix(browser-vm): clean up completed timeout records

[2heal1]

Summary

• Remove completed one-shot timers from sandbox tracking.
• Clear timer and interval records during sandbox recovery.
• Preserve callback arguments, callback context, and string handler support.
• Add regression tests for timer cleanup behavior.

Problem

The browser-vm timer module retained timeout records after their callbacks had already completed. In long-lived sandboxes, these stale records could accumulate until the JavaScript engine reached the Set size limit and threw:

RangeError: Set maximum size exceeded

Testing

• All 55 browser-vm tests passed.
• All 5 timer regression tests passed.
• The browser-vm package build passed.
• Formatting and code checks passed.

[vercel]

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