Work around MSVC error

MSVC is complaining that `using default_sequence_traits::for_each_while` in `drop_adaptor::sequence_traits` references an unknown base class, which doesn't make a lot of sense as it very definitely does inherit from it... but never mind, we'll work around it anyway

include/flux/op/drop.hpp

@@ -54,7 +54,10 @@ struct drop_adaptor : inline_sequence_base<drop_adaptor<Base>> {
             return flux::data(self.base()) + (cmp::min)(self.count_, flux::size(self.base_));
         }
 
-        using default_sequence_traits::for_each_while;
+        static constexpr auto for_each_while(auto& self, auto&& pred) -> cursor_t<Base>
+        {
+            return default_sequence_traits::for_each_while(self, FLUX_FWD(pred));
+        }
     };
 };