Function logos_floordiv_exact 

pub fn logos_floordiv_exact(
    a: impl Into<LogosInt>,
    b: impl Into<LogosInt>,
) -> LogosInt

Floor division — the quotient rounded toward NEGATIVE INFINITY (-7 // 2 → -4), the // operator. Loud canonical panic on a zero divisor; exact (promotes to BigInt). Distinct from logos_div_exact, which truncates toward zero.