Network: clique

We must be able to force the `Network` to create "cliques." These are groups of nodes for which the probability of communicating with each other is much higher than with nodes outside of the clique. The number, size, and likelihood of clique communication vs external communication must be configurable.

Start by locating the Network entry point and its configuration and simulation code. Determine how node-to-node communication probability is currently modeled. Done means configurable clique count, clique size, and the relative probability of communication within versus outside each clique, with behavior covered by tests.

Written by the indexing model from the issue text.