[FEATURE] make apply sfinae friendly about kumi HOT 1 CLOSED

somewhat related, the sfinae for for_each is not completely correct

struct A {
  void operator()(auto&&) & {}
};

struct B {
  void operator()(auto&&) && {}
};

auto main() -> int {
  A a;
  B b;
  kumi::for_each(a, kumi::make_tuple(1,2));
  kumi::for_each(b, kumi::make_tuple(1,2));
}

the first for_each fails, when it should succeed
the second for_each fails, but inside the function (for_each) instead of at the sfinae boundary

the sfinae condition should be _::applicable<Function&, Tuple, Tuples...> instead of _::applicable<Function, Tuple, Tuples...>

from kumi.