feat(人物): 更新熊角色属性和资源文件

- 将熊角色贴图从JPG格式替换为PNG格式
- 调整熊角色的攻击冷却时间和冲刺逻辑
- 修改熊角色的碰撞体积和状态条位置
- 简化测试波次配置，仅保留熊角色
- 为阶段转换添加无敌状态
- 提高小鸡角色的冲刺倍率

scripts/Statemachine/EntityBase.gd

@@ -175,6 +175,7 @@ func timeLived():
 func setStage(stage: int):
 	if currentStage == stage:
 		return
+	currentInvinsible = true
 	canRunAi = false
 	var oldStage = currentStage
 	currentStage = stage
@@ -185,6 +186,7 @@ func setStage(stage: int):
 	stageAnimator.play("enter")
 	await stageAnimator.animation_finished
 	canRunAi = true
+	currentInvinsible = false
 func applyLevel():
 	fields[FieldStore.Entity.MAX_HEALTH] *= (1 + GameRule.entityHealthIncreasePerWave * (GameRule.difficulty + 1)) ** level
 	fields[FieldStore.Entity.DAMAGE_MULTIPILER] *= (1 + GameRule.entityDamageIncreasePerWave * (GameRule.difficulty + 1)) ** level