Add 2-sample tests under ER, SBM, density adjusted SBM models

[bdpedigo]

I have been developing 2-sample tests under an ER or SBM assumption here: https://github.com/neurodata/bilateral-connectome

Considering adding these as functions to the inference submodule.

Would be more inclined to do so if we have other applications where these could be useful - for instance, @ebridge2 I thought I saw you using in the book?

[bdpedigo]

@aj-hersko this would take explanation but is a potential project