Make this function smaller

[recmo]

On 2020-04-29 @pvienhage wrote in 7850bac “Smart contrat Recurance proof system impl (#677)”:

Make this function smaller

        res.push_str("]");
        res
    }
}

// TODO - Make this function smaller
#[allow(clippy::too_many_lines)]
pub fn proof_serialize(
    constraints: &Constraints,
    proof: &Proof,
    result_string: &mut String,

From crypto/stark/src/solidity_seralizer.rs:54