Resolve precedence clippy lint
Resolve precedence clippy lint

    error: operator precedence can trip the unwary
      --> src/udiv128.rs:15:17
       |
    15 |     let high2 = x_hi as u128 * y_lo as u128 + m_lo as u128 >> 64;
       |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider parenthesizing your expression: `(x_hi as u128 * y_lo as u128 + m_lo as u128) >> 64`
       |
       = note: `-D clippy::precedence` implied by `-D clippy::all`
       = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#precedence

dtolnay/itoa