use non-block form of Dir.mktmpdir for speed as it avoids unneeded /tmp cleanup
use non-block form of Dir.mktmpdir for speed as it avoids unneeded /tmp cleanup

cyber-dojo/runner_stateless,cyber-dojo/runner_stateless,cyber-dojo/runner,cyber-dojo/runner_stateless,cyber-dojo/runner_stateless,cyber-dojo/runner_stateless,cyber-dojo/runner_stateless,cyber-dojo/runner_stateless,cyber-dojo/runner