Support for getting natures by index for iterating purposes.

src/Library/Natures/NatureLibrary.hpp

@@ -42,6 +42,11 @@ namespace PkmnLib::Library {
             }
             throw CreatureException("Nature not found.");
         }
+
+        size_t GetNatureCount() const noexcept { return _items.size(); }
+        inline const ArbUt::StringView& GetNatureFromIndex(size_t index) const {
+            return std::next(std::begin(_items), index)->first;
+        }
     };
 }