Add extra value_type() construction in range-based iterator insertion so implicitly convertible types are supported, i.e. test::proxy

include/boost/unordered/unordered_flat_map.hpp

@@ -189,7 +189,7 @@ namespace boost {
       void insert(InputIterator first, InputIterator last)
       {
         for (auto pos = first; pos != last; ++pos) {
-          table_.insert(*pos);
+          table_.insert(value_type(*pos));
         }
       }