Add function to set variants for a species, and a function to get the count of species in a species library.

src/Library/CreatureData/CreatureSpecies.hpp

@@ -39,6 +39,8 @@ namespace CreatureLib::Library {
         [[nodiscard]] const SpeciesVariant* GetVariant(const std::string& key) const;
         [[nodiscard]] Gender GetRandomGender(Core::Random& rand) const;
         [[nodiscard]] const std::string& GetName() const;
+
+        void SetVariant(const std::string& name, const SpeciesVariant* variant) { _variants[name] = variant; }
     };
 }