Rethink getPsiMinv and dummy_vmt in DiracDeterminantBase

[ye-luo]

Under "#ifndef NDEBUG" is potentially problematic. Prefer read-only access to the inverse matrix as a feature not just for debugging.

[PDoakORNL]

I will revisit a the possibility of a const view and psiMinv ownership after the different accelerated flavors of direct inversion are in.