Function group_utxos_by_txid

pub fn group_utxos_by_txid(
    utxos: impl IntoIterator<Item = Utxo>,
) -> BTreeMap<Txid, Vec<OutputEntry>>

Groups UTXOs by txid into a lexicographically ordered BTreeMap (same as the order stored by Bitcoin Core in leveldb).

NOTE: this requires substantial RAM.