Add ticking elapsed time on "initial time measurement"

It would be helpful to see the elapsed time on the initial time measurement.

Right now, I have a very long running benchmark subject sitting at "Initial time measurement" and "ETA 00:00:00"; I'd love to see the elapsed time ticking at least in this case, e.g. as " AT 00:10:23", indicating that hyperfine is 10 minutes 23 seconds into the initial run.