message: Use pow instead of checked_pow
diff: use schemars::JsonSchema;
  use serde::{de, ser, Deserialize, Deserializer, Serialize};
  -use std::convert::{TryFrom, TryInto};
  +use std::convert::TryFrom;
  use std::fmt::{self, Write};
  use std::iter::Sum;
  use std::ops;
  @@ -82,9 +82,8 @@ impl FromStr for Decimal {
  let exp = (18usize.checked_sub(fractional_part.len())).ok_or_else(|| {
  StdError::generic_err("Cannot parse more than 18 fractional digits")
  })?;
  - let fractional_factor = 10u128
  - .checked_pow(exp.try_into().unwrap())
  - .ok_or_else(|| StdError::generic_err("Cannot compute fractional factor"))?;
  + debug_assert!(exp <= 18);
  + let fractional_factor = 10u128.pow(exp as u32);
  atomics = atomics
  .checked_add(fractional * fractional_factor)
  .ok_or_else(|| StdError::generic_err("Value too big"))?;
  