Clad fails to use proper pullbacks for functions with reference arguments

[gojakuch]

reproducer

#include "clad/Differentiator/Differentiator.h"
#include <iostream>

#define show(x) std::cout << #x << ": " << x << "\n";

double fff(double &x) {
    return 0;
}

double fn(double u, double v) {
    double &w = u;
    fff(u);
    return v;
}

int main() {
    auto d_fn = clad::gradient(fn);
    double u = 3, v = 5;
    double du, dv;
    du = dv = 0;
    show(fn(u, v));
    d_fn.execute(u, v, &du, &dv);
    show(du);
    show(dv);
}

an important note, same should work out for constructors:

#include "clad/Differentiator/Differentiator.h"
#include <iostream>

#define show(x) std::cout << #x << ": " << x << "\n";

class SafeTestClass {
    public:
    SafeTestClass() {};
    SafeTestClass(double &x) {
    }
};

namespace clad {
namespace custom_derivatives {
namespace class_functions {
    clad::ValueAndAdjoint<SafeTestClass, SafeTestClass>
    constructor_reverse_forw(clad::ConstructorReverseForwTag<SafeTestClass>, double& x, double *d_x) {
        return {SafeTestClass(x), SafeTestClass(*d_x)};
    }
    void constructor_pullback(SafeTestClass *c, double &x, SafeTestClass *d_c, double* d_x) {
        
    }
}}}

double fn(double u, double v) {
    double &w = u;
    SafeTestClass s3(w);
    return v;
}

int main() {
    auto d_fn = clad::gradient(fn);
    double u = 3, v = 5;
    double du, dv;
    du = dv = 0;
    show(fn(u, v));
    d_fn.execute(u, v, &du, &dv);
    show(du);
    show(dv);
}

[gojakuch]

the first reproducer might actually be related to #1105