Track first_seen #1947
Description
Describe the enhancement
Add a first_seen field to tx_graph::ChangeSet and a way to retrieve the first-seen timestamp for a transaction.
Use case
Currently, tx_graph::ChangeSet only tracks the last_seen timestamp. last_seen is useful for canonicalization. However, wallets would like to order unconfirmed transactions by first_seen so that the wallet user sees a chronological list of transactions in their transaction list.