Cardano Updates

* Verification of `PrevGovActionId` in `proposalsAddAction` happens on
  accumulated `proposals`
* While `preceedingHardFork` check happens on original `st`.

In a usual application, which has identifiers assigned, this inconsistency
would be a problem. However, in a transaction`GovActionId` is derived from
a hash of a transaction itself. This means that it is impossible to reference
a previous governance action within the same transaction, since you'd need to
know a hash of a transaction that contains the proposal itself.

Therefore, this commit fixes not an issue, but a mere inconsistency.
This is done in order to avoid developers even considering this edge case.

to match the spec

to fix the tests failing because of the new predicate failure

Consolidates golden tests from the separate `cardano-ledger-alonzo-test`
package into the main `cardano-ledger-alonzo` impl package, following the
same pattern already completed in other eras (allegra, mary, conway, babbage).

Added in order to be able to apply some function on the `txAuxData`
field of a transaction even when the `txAuxData` field is set to
`SNothing`.