fn inv(a: &[FieldElement<F>; 2]) -> Result<[FieldElement<F>; 2], FieldError> {
        let inv_norm = (a[0].pow(2_u64) - Q::residue() * a[1].pow(2_u64)).inv()?;
        Ok([&a[0] * &inv_norm, -&a[1] * inv_norm])
    }
Returns the multiplicative inverse of `a`
This uses the equality `(a0 + a1 * t) * (a0 - a1 * t) = a0.pow(2) - a1.pow(2) * Q::residue()`
crates/math/src/field/extensions/quadratic.rs