message: fix: Use constant to simplify code
diff: @@ -282,10 +282,10 @@ impl EpochNumberWithFraction {
  }
  pub fn number(&self) -> u64 {
  - (self.0 >> 16) & ((1u64 << 40) - 1)
  + (self.0 >> Self::FRACTION_BITS) & Self::NUMBER_MASK
  }
  pub fn fraction(&self) -> u64 {
  - u64::from(self.0 as u16)
  + self.0 & Self::FRACTION_MASK
  }
  }
  