Use SignableState throughout entire state lifecycle

This should be done after https://github.com/hashgraph/hedera-services/issues/6216

We currently wrap `State` objects in a `SignableState` objects only once they become immutable. It would be better to wrap all states, even the mutable state, in a `SignableState` object. This gives us more coherent APIs, as well as enabling the traceability tooling for `SignableState` reference count errors for all states in the system.