Store CreatureIndex on Creature, includes helper function to get a creatures party from a battle.

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

src/Battling/Models/Battle.hpp

@@ -85,6 +85,8 @@ namespace CreatureLib::Battling {
         inline const BattleResult& GetResult() const noexcept { return _battleResult; }
 
         const ArbUt::UniquePtrList<BattleParty>& GetParties() const noexcept { return _parties; }
+        ArbUt::OptionalBorrowedPtr<BattleParty> FindPartyForCreature(const ArbUt::BorrowedPtr<Creature>&);
+
         const ArbUt::UniquePtrList<BattleSide>& GetSides() const noexcept { return _sides; }
         ArbUt::OptionalBorrowedPtr<BattleScript> GetVolatileScript(const ArbUt::StringView& key) const {
             return _volatile.Get(key);