GC stops the entire JVM, so it does "double count" but these are IMO correct. The main point here is to make it easy to see if a slow task is caused by a GC pause.

We can add total time spent in GC as well in a subsequent PR. It's a bit confusing how you should count the total though... for instance do you "double count" or not, if multiple tasks are running during a GC event. Another useful thing to add would be at the executor level add a metric for what proportion of overall time is spent in GC.