Add globally configured repo-wide test variants

[ssalbdivad]

Ideas that come to mind:

• jitless:

  • very high ROI since it's a totally different code path, but would need a way to account for a few expected differences in snapshots e.g. because jitless mode does not traverse discriminants yet

• inverted:

  • default invert on intersections to true for morphless intersections. Also likely needs a way to account for differences or ignored tests, but would ensure commutativity is robust