feat(electrum): include option for previous TxOuts for fee calculation

The previous `TxOut` for transactions received from an external
wallet may be optionally added as floating `TxOut`s to `TxGraph`
to allow for fee calculation.

example-crates/wallet_electrum/src/main.rs

@@ -53,7 +53,7 @@ fn main() -> Result<(), anyhow::Error> {
         .inspect_spks_for_all_keychains(|_, _, _| std::io::stdout().flush().expect("must flush"));
 
     let mut update = client
-        .full_scan(request, STOP_GAP, BATCH_SIZE)?
+        .full_scan(request, STOP_GAP, BATCH_SIZE, false)?
         .with_confirmation_time_height_anchor(&client)?;
 
     let now = std::time::UNIX_EPOCH.elapsed().unwrap().as_secs();