fn inv(a: &Self::BaseType) -> Result<Self::BaseType, FieldError> {
        let inv_norm = (a[0].square() + a[1].square()).inv()?;
        Ok([&a[0] * &inv_norm, -&a[1] * inv_norm])
    }
Returns the multiplicative inverse of `a`
This uses the equality `(a0 + a1 * u) * (a0 - a1 * u) = a0.pow(2) - a1.pow(2) * residue()`
crates/math/src/elliptic_curve/short_weierstrass/curves/bn_254/field_extension.rs