test.sh: Autoparallelise the testsuite as possible
test.sh: Autoparallelise the testsuite as possible

On my workstation, this yields a 4× reduction in test time in the dev profile,
and almost 8× under the CI test profile.  The difference is that Hypothesis run
each test 10 times (w/ different random inputs) in dev and 1k time in CI.

ppb/ppb-vector,ppb/ppb-vector