message: Fix Uint256::try_from(&str) to expect dec values
diff: @@ -178,7 +178,7 @@ impl TryFrom<&str> for Uint256 {
  type Error = StdError;
  fn try_from(val: &str) -> Result<Self, Self::Error> {
  - match val.parse::<U256>() {
  + match U256::from_dec_str(val) {
  Ok(u) => Ok(Uint256(u)),
  Err(e) => Err(StdError::generic_err(format!("Parsing u256: {}", e))),
  }
  @@ -398,10 +398,7 @@ impl<'de> de::Visitor<'de> for Uint256Visitor {
  where
  E: de::Error,
  {
  - match U256::from_dec_str(v) {
  - Ok(u) => Ok(Uint256(u)),
  - Err(e) => Err(E::custom(format!("invalid Uint256 '{}' - {}", v, e))),
  - }
  + Uint256::try_from(v).map_err(|e| E::custom(format!("invalid Uint256 '{}' - {}", v, e)))
  }
  }
  @@ -447,7 +444,7 @@ mod tests {
  assert_eq!(a.0, U256::from(5));
  let result = Uint256::try_from("34567");
  - assert_eq!(result.unwrap().0, U256::from("34567"));
  + assert_eq!(result.unwrap().0, U256::from_dec_str("34567").unwrap());
  let result = Uint256::try_from("1.23");
  assert!(result.is_err());
  