message: add function for the State to display the total
diff: use super::utxo::{UTxO, UTxOs};
  use super::log::{Log};
  use super::{lookup::{AddressLookup}, ptr::StatePtr};
  -use cardano::{tx::TxIn};
  +use cardano::{tx::TxIn, coin::{self, Coin}};
  use std::{fmt};
  #[derive(Debug)]
  @@ -18,6 +18,15 @@ impl<T: AddressLookup> State<T> {
  pub fn ptr<'a>(&'a self) -> &'a StatePtr { &self.ptr }
  + pub fn total(&self) -> coin::Result<Coin> {
  + self.utxos
  + .iter()
  + .map(|(_, v)| v.credited_value)
  + .fold(Ok(Coin::zero()), |acc, v| {
  + acc.and_then(|acc| acc + v)
  + })
  + }
  +
  /// update the wallet state with the given logs
  /// This function is for initializing the State by recovering the logs.
  ///
  