Wire `snapshots/v0` namespace into cardano-ledger repo

[qnikst]

We need snapshots/v0 namespace to be supported in the cardano-ledger code.

In order to achieve that we need:

• ensure that the CDDL types do not contradict with the ledger types (i.e. has all required information, do not have extra information that can be derived)
• on-chain types persist the structure as much as possible (really that should be kept as-is because hashes calculation require exactly the same binary representation)
• for each non BaseType and non on-chain type a proxy is introcuced
• the code follows the structure requirements that would be created during communication with ledger team.