Consider sharing randomx cache and dataset between prover and verifier

[poszu]

Currently, there are separate instances of RandomX cache and dataset on proving and verifying path. In some cases, it could make sense to share them. For example, when a verifier is configured in FAST mode (2GB), then it could share its dataset with the prover.

Doing it in the other direction (to share a dataset with the verifier) makes less sense as a prover is created once every epoch and it exists only for a short time.