feat(game): add elite monster kill statistics and related fields

1. add is_elite field to HeroAttrsComp for elite monster mark
2. set elite monster flag when spawning mission monsters
3. implement monster kill counting logic with priority: Boss > elite > normal monsters
4. add kill count statistics for different monster types for settlement calculation

assets/script/game/map/MissionMonComp.ts

@@ -240,6 +240,8 @@ export class MissionMonCompComp extends CCComp {
             model.ap = monData.ap;
             model.hp_max = monData.hp;
             model.hp = model.hp_max;
+            // 精英标记：对象池复用实体需显式重置（Boss 与精英互斥，Boss 走 is_boss）
+            model.is_elite = !monData.isBoss && !!monData.isElite;
         }
 
         this.sectionSpawnedCount++;