Model the data distribution across nodes

[leobago]

The idea is to model the Codex platform with as much detail as possible so that we can make projections about failure rates, rebuild overheads, the marketplace, attack mitigations, and other important aspects of it.

A first plan covering some aspects of the model is here: https://hackmd.io/yTRlMInIRi6fG-nk984ULQ