Heuristic to find a nice ergonomic number of jobs to do in parallel by
default.
If we use ALL the available CPUs, then that can actually make tests more
flaky in some cases, because things will start to drag.
Especially, if there's a ton of CPUs, like on a hosted CI system, we don't
want to flood the system too aggressively, since memory may be constrained.
But, we do want to parallelize tests quite a bit by default, as this can
speed things up considerably.
Heuristic to find a nice ergonomic number of jobs to do in parallel by default.
If we use ALL the available CPUs, then that can actually make tests more flaky in some cases, because things will start to drag.
Especially, if there's a ton of CPUs, like on a hosted CI system, we don't want to flood the system too aggressively, since memory may be constrained. But, we do want to parallelize tests quite a bit by default, as this can speed things up considerably.