scoped: declare copy and move constructors

they aren't defined currently because we haven't needed them. this is
just to avoid accidents where the defaults will prove problematic.

scoped.hpp

@@ -87,9 +87,8 @@ namespace util::scoped {
             m_args (std::forward<Args> (_args)...)
         { ; }
 
-
-        void disable (void) { m_enabled = false; }
-
+        function (function&&);
+        function (const function&);
 
         ~function ()
         {
@@ -97,6 +96,8 @@ namespace util::scoped {
                 std::apply (std::move (m_function), std::move (m_args));
         }
 
+        void disable (void) { m_enabled = false; }
+
     private:
         bool m_enabled = true;
         FuncT m_function;