pub fn common(self) -> bool {
    // The block rewards for epochs 0 through 9 are all multiples
    // of 9765625 (the epoch 9 reward), so any sat from epoch 9 or
    // earlier that isn't divisible by 9765625 is definitely common.
    if self < Epoch(10).starting_sat() && self.0 % Epoch(9).subsidy() != 0 {
      return true;
    }

    // Fall back to the full calculation.
    let epoch = self.epoch();
    (self.0 - epoch.starting_sat().0) % epoch.subsidy() != 0
  }
Is this sat common or not?  Much faster than `Sat::rarity()`.
crates/ordinals/src/sat.rs