Previously, scrapes durations that are very short (e.g., connection refused)
could show as empty (durations under 1 millisecond).
This commit ensures that sub-millisecond durations are correctly
displayed as "0ms" or "1ms" when necessary.
- Adjusted `humanizeDuration` to round sub-millisecond durations to the
nearest millisecond.
- Updated unit tests to verify the correct handling of sub-millisecond
values.
Signed-off-by: Julien <roidelapluie@o11y.eu>