Replace Padder CRTP base with a concept.

Chaos/Padding/PadderPkcs7.hpp

@@ -13,7 +13,7 @@
 namespace Chaos::Padding
 {
 
-class PadderPkcs7 : public Padder<PadderPkcs7>
+class PadderPkcs7
 {
 public:
     template<typename OutputIt>
@@ -75,6 +75,8 @@ private:
     using Branchless = Service::Branchless;
 };
 
+static_assert(Padder<PadderPkcs7>);
+
 } // namespace Chaos::Padding
 
 #endif // CHAOS_PADDING_PADDERPKCS7_HPP