[ADP-3215] Add TxOut type to Cardano.Wallet.Read.Tx

[HeinrichApfelmus]

This pull request adds a type TxOut to Cardano.Wallet.Read.Tx.TxOut.

The type TxOut occupies the following point in the design space:

• TxOut is era-independent — a value of this type can be any transaction output from a past era.
• TxOut can — in principle — be deconstructed using functions from the latest or next era. This is possible because transaction outputs are upwards-compatible.
• TxOut can be serialized and deserialized to a format that is close to the ledger CBOR. However, we allow serialize . deserialize ≠ id in order to allow internal era upgrades.

The above design choices can be realized with different internal representations. We choose the following:

• TxOut is represented as a disjoint sum of Output era.
• TxOut supports explicit an upgrade to Output era where era is the latest or next era — but this conversion is not zero-cost.

Comments

• In addition to deconstruction, we also provide a constructor mkBasicTxOut for convenience and testing.

Issue Number

ADP-3215

[Anviking]

first look

[HeinrichApfelmus]

As discussed, I have

• removed the instance Eq TxOut
• reimagined the upgrade function as upgradeTxOutToBabbageOrLater
• added a test case that describes the Conway treatment of invalid stake pointers

In lieu of the tests relating to toConwayTxOut and toBabbageTxOut, I have also

• added a test case that upgradeTxOutToBabbageOrLater preserves getValue

In the interest of development time, I have refrained from adding further tests on upgradeTxOutToBabbageOrLater, especially relating to the Byron era — I think the code is self-explanatory enough so that additional testing provides diminishing returns.