chore: Add a space in debug log for duration

[lym953]

Right now we have debug log like Flushing traces took 50ms. This PR adds a space between 50 and ms so it's easier to process the log. For example, we can use echo 'Flushing traces took 50 ms' | awk '{print $4}' to extract the 50.

[astuyve]

This is fine, worth noting that this is printing wall clock time which may not equal CPU time, and some measurements span async work over multiple invocations