Function toString

tests/unit/operations.cpp:629–636

// and/or re-use printer_ functions as much as possible

std::string toString(vector<int> list) {

    std::string out = "{ ";
    for (int& e : list)
        out += std::to_string(e) + " ";
    out += "}";
    return out;
}

std::string toString(PauliStr str, vector<int> targs) {