Build out and test a version of patternDrivers using VGAM DE testing.

[Loyale]

To identify features outside of the feature map that are associated with projected weights, we want to implement a version of patternDrivers (or call it another test) where we do a DE gene test in the target gene expression space (after projection from source) using VGAM with appropriate family (negbinomial). This would be a 'standard' DE gene test using estimated P-weights from a projection as an explanatory variable. The goal is to identify genes in the target space whose expression is a function of P-weights for interesting/significant patterns.