Overhaul memory model to new Arbutils memory.

Signed-off-by: Deukhoofd <Deukhoofd@gmail.com>

src/Library/CreatureData/LearnableAttacks.hpp

@@ -36,7 +36,7 @@ namespace CreatureLib::Library {
         /// @brief Returns a random attack that can be learned.
         /// @param rand A random number generator.
         /// @return A random attack that can be learned.
-        virtual ArbUt::BorrowedPtr<const AttackData> GetRandomAttack(ArbUt::Random& rand) const;
+        virtual std::optional<ArbUt::BorrowedPtr<const AttackData>> GetRandomAttack(ArbUt::Random& rand) const;
     };
 }