Finish the `Family.Values` functionality

[blamario]

The Family.Values module is currently the only part of the transaction-family-specification library that depends on Cardano. Or rather, it should depend on it but doesn't yet, because the whole library requires GHC 9. I created a small shim instead at Family.Ledger to export the relevant type names.

Now that Plutus and Cardano are finally upgrading to GHC 9:

• [ ] this shim should be replaced with proper imports,
• [ ] the library should be nixified to keep track with IOG,
• [ ] a new TxSpecimen -> Tx function should be added, where the result Tx is either the one from plutus-ledger-api or from plutus-simple-model.

[blamario]

More precisely, the new function's signature would have to be something like

Transaction t => Environment t -> TxSpecimen t -> Tx

where the purpose of Environment is to provide things like a mapping of the specified Scripts to actual PlutusTx scripts.