fix: 修复技能属性引用问题并移除无用代码

- 在Skill.ts中修改Attrs为浅拷贝避免引用问题
- 移除HeroAtk.ts中未使用的casterModel变量

assets/script/game/skill/Skill.ts

@@ -90,7 +90,7 @@ export class Skill extends ecs.Entity {
         const sDataCom = this.get(SDataCom);
         sDataCom.group=caster.box_group
         sDataCom.caster=caster
-        sDataCom.Attrs=cAttrsComp.Attrs
+        sDataCom.Attrs={...cAttrsComp.Attrs}
         sDataCom.s_uuid=s_uuid
         sDataCom.fac=cAttrsComp.fac
     }