feat(applying): certificate and native script validation for ShelleyMA

[sterraf]

This PR implements checks for

• the execution of native scripts; and
• validity of certificates;

for ShelleyMA. This also required a revision of check_preservation_of_value to take care of pool deposits and the like. (The implementation of native scripts has also been been tested at Alonzo, but will be included in a future PR).

I tried to follow the specs for the Shelley and Mary ledgers. In order to do this, I implemented (with guidance by Gadea) some of the relevant types that describe the “states” related by the different transition relations governing the ledger (see utils.rs); v.g. DState records key delegations and pointers, etc.

Breaking change

In order to make use of the new checks, validate_shelley_ma_tx (and hence validate, which has been renamed to validate_txs and takes a list of transactions) must maintain (and modify) those states, and hence the type signature differs from the original one.

API

The original (mutable) state must be preserved before checking a tx (e.g. at Dolos) with validate_txs:

let mut buf_state: CertState = state.clone();
match validate_txs(..., &buf_state) {
	Ok(()) => state = buf_state,
	Err(error) =>  // handle error,
};

This is because the buffer state will end up inconsistent in case of a validation error.

Tests

Eight new unit tests (four positive and four negative) were added.