Overload resolution failure in `PRO_DEF_FREE_AS_MEM_DISPATCH`

[mingxwa]

Repro:

#include <functional>

#include <proxy/proxy.h>

PRO_DEF_FREE_AS_MEM_DISPATCH(MemInvoke, std::invoke, invoke);

struct Invocable : pro::facade_builder
    ::add_convention<MemInvoke, void(), void(int)>
    ::build {};

int main() {
  pro::proxy<Invocable> p = pro::make_proxy<Invocable>([](auto...) {});
  p->invoke();
}

Compiler output (clang 21.1.5, -O2 -Wall -std=c++23):

test.cpp:13:6: error: member 'invoke' found in multiple base classes of different types
   13 |   p->invoke();
      |      ^
test.cpp:5:54: note: member found by ambiguous name lookup
    5 | PRO_DEF_FREE_AS_MEM_DISPATCH(MemInvoke, std::invoke, invoke);
      |                                                      ^
test.cpp:5:54: note: member found by ambiguous name lookup
1 error generated.

Regression caused by: #320