chore(state): Save validator set in shim layer state

Currently, Emerald always asks the smart contract for the current validator set. Ideally we should have this state in our local DB to avoid calls to fetch the valset.

These entries would be added to the database on start of the node and when the validator set changes.
Possible we'd have to still call into the execution engine on `Decided` but we will save calls in other places.