upcastable renamed to upcast_base

src/include/units/unit.h

@@ -29,7 +29,7 @@ namespace units {
 
   template<Dimension D, Ratio R>
     requires (R::num > 0)
-  struct unit : upcastable<unit<D, R>> {
+  struct unit : upcast_base<unit<D, R>> {
     using dimension = D;
     using ratio = R;
   };