[shuffle_v2] insufficient we_ tests

[DenisYaroshevskiy]

In the generic shuffle_v2 testing framework we should plugin some w/e mix ins.
It's ofc going to be both expensive and incomplete but with shuffles there is always a limit to what we can test

NOTE: generic idxm (index math) stuff is mostly tested for we_. But platform specific idxm is not tested by itself, without the shuffles - so there is probably bugs.