fix(tx_graph)!: Change tx_last_seen to Option<u64>

Also fixup `test_list_owned_txouts` to check that the right
outputs, utxos, and balance are returned at different local
chain heights.

This fixes an issue where unbroadcast and otherwise non-canonical
transactions were returned from methods `list_chain_txs` and
`Wallet::transactions` because every tx inserted had a last_seen
of 0 making it appear unconfirmed.

Note this commit changes the way `Balance` is represented due to
new logic in `try_get_chain_position` that no longer considers
txs with non-canonical anchors. Before this change, a tx anchored
to a block that is reorged out had a permanent effect on the
pending balance, and now only txs with a last_seen time or an
anchor confirmed in the best chain will return a `ChainPosition`.

crates/electrum/tests/test_electrum.rs

@@ -198,17 +198,14 @@ fn tx_can_become_unconfirmed_after_reorg() -> anyhow::Result<()> {
             .apply_update(update.chain_update)
             .map_err(|err| anyhow::anyhow!("LocalChain update error: {:?}", err))?;
 
-        // Check to see if a new anchor is added during current reorg.
-        if !initial_anchors.is_superset(update.graph_update.all_anchors()) {
-            println!("New anchor added at reorg depth {}", depth);
-        }
+        // Check that no new anchors are added during current reorg.
+        assert!(initial_anchors.is_superset(update.graph_update.all_anchors()));
         let _ = recv_graph.apply_update(update.graph_update);
 
         assert_eq!(
             get_balance(&recv_chain, &recv_graph)?,
             Balance {
                 confirmed: SEND_AMOUNT * (REORG_COUNT - depth) as u64,
-                trusted_pending: SEND_AMOUNT * depth as u64,
                 ..Balance::default()
             },
             "reorg_count: {}",