Add support for swapping in and out of a party.

src/Battling/Models/CreatureParty.hpp

@@ -23,6 +23,12 @@ namespace CreatureLib::Battling {
             _party[b] = ca;
         }
 
+        Creature* SwapInto(size_t index, Creature* creature) {
+            auto p = _party.TakeOwnership(index);
+            _party.Set(index, creature);
+            return p;
+        }
+
         bool HasAvailableCreatures() const noexcept {
             for (Creature* c : _party) {
                 if (c == nullptr)