increase confidence on results by adding statistical tests on different class partitions

[oreparaz]

We could do some sanity checks to make sure we're not catching (statistical) ghosts:

• statistical test on a random partition of one group (all corresponding to the same input). should not yield any statistical difference
• idem, for the second group
• idem, for a random partition of the set of all traces.

These tests should all return "no leakage detected". I'd say this isn't super high priority, please check-in here before if you're interested in working on this.