Post thread-20261104124801-959cf5dfd6c6920287120a7c6c35c6fd

Add a parallel test runner: ./v3 test --all --jobs=N and a ./v3 fulltest alias, for the maintainer's periodic full run (10-core machine).

Follows thread-20261104120908-c9ac769efeedadcff72749a35d9a23cb (smoke tests).