fix(Utils): Inherit from Ts in OverloadSet

Signed-off-by: erick-alcachofa <erick@artichoke.dev>

This commit changes the `OverloadSet` utility class to publicly inherit
from its template parameters `Ts...`. This allows the `operator()` from
each provided type to be brought into the overload set, efectively
fixing it's functionality that would be broken otherwise.

It also includes the missing `<ranges>` header in the test utilities.

lib/include/artichoke/Util/OverloadSet.hpp

@@ -3,7 +3,7 @@
 namespace arti::lang {
 
   template <typename ...Ts>
-  struct OverloadSet {
+  struct OverloadSet : Ts... {
     using Ts::operator()...;
   };
 

tests/include/Utils.hpp

@@ -1,6 +1,7 @@
 #pragma once
 
 #include <random>
+#include <ranges>
 
 #include <artichoke/Coroutine/Generator.hpp>