[Chronik] Add GroupUtxoWriter and GroupUtxoReader

Summary:
Update UTXO set for each group member.

We store a list of ordered UTXOs (sorted by tx_num, then out_idx) for each group member.

We also also attach the value to each UTXO, which allows us to return the UTXO set for scripts very efficiently, without having to look up the spent tx from the node.

It's unclear at this point whether this is useful for other kinds of groups, but if it isn't, we can make UtxoEntry more generic in the future.

Depends on D13717.

Test Plan: ninja check-crates

Reviewers: Fabien, #bitcoin_abc

Reviewed By: Fabien, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D13718