feat(compare): comform_to func and odering_like concept

Closes #20

Author: c0nstexpr

include/stdsharp/compare/compare.h

@@ -6,14 +6,22 @@
 
 namespace stdsharp
 {
+    template<typename Cat>
+    concept ordering_like =
+        same_as_any<Cat, std::partial_ordering, std::weak_ordering, std::strong_ordering>;
+
     constexpr bool is_ud(const std::partial_ordering c) noexcept
     {
         return c == std::partial_ordering::unordered;
     }
 
+    constexpr bool comform_to(const std::partial_ordering l, decltype(l) r) noexcept
+    {
+        return is_eq(l) || l == r;
+    }
+
     template<typename Fn, typename T, typename U, typename Cat = std::partial_ordering>
-    concept ordering_predicate =
-        std::convertible_to<Cat, std::partial_ordering> && invocable_r<Fn, Cat, T, U>;
+    concept ordering_predicate = ordering_like<Cat> && invocable_r<Fn, Cat, T, U>;
 
     template<typename Fn, typename T, typename U, typename Cat = std::partial_ordering>
     concept nothrow_ordering_predicate =