Return previous value from Set function.

src/Collections/List.hpp

@@ -52,7 +52,9 @@ namespace Arbutils::Collections {
                 throw std::logic_error(ss.str());
             }
 #endif
+            auto prev = _vector.at(index);
             _vector[index] = value;
+            return prev;
         }
 
         inline bool Contains(const ValueT& value) const {