Linked issue

Fixes #6583

Type of change

• Bug fix (non-breaking change that fixes an issue)

Motivation

Floating-point truncation causes Int(0.999...) → 0, so sleep(1e-9) returns immediately.

What changed

Replace Int() with round() in the fractional-seconds-to-nanoseconds conversion.

Testing

All tests pass, including new cases for sub-second sleep durations (e.g., 1ms).

Checklist

• The linked issue above has been reviewed by a maintainer and is
  agreed-upon, or this is a trivial fix that does not need prior
  approval
• PR is small and focused — I've split larger changes into a sequence of
  smaller PRs where possible (see
  pull request sizes)
• I ran ./bazelw run format to format my changes
• I added or updated tests to cover my changes
• If AI tools assisted with this contribution, I have included an
  Assisted-by: trailer in my commit message or this PR description (see
  AI Tool Use Policy)
  Assisted-by: AI