refactor(BulletBase): 重构子弹分裂和折射逻辑，移除parentScene字段

将子弹分裂和折射的逻辑从静态生成方法改为实例克隆方式，简化代码结构并提高可维护性。移除不再使用的parentScene字段，相关功能通过克隆实例实现。

scripts/Statemachine/BulletBase.gd

@@ -35,7 +35,6 @@ var isChildRefract: bool = false
 var initialSpeed: float = 0
 var initialDamage: float = 0
 var speedScale: float = 1
-var parentScene: PackedScene = null
 var isFirstFrame: bool = true
 
 func _ready():
@@ -150,7 +149,9 @@ func trySplit():
 		var total = MathTool.shrimpRate(value)
 		var last = value - floor(value)
 		for i in total:
-			split(i, total, last)
+			var cloned = duplicate() as BulletBase
+			cloned.rotation = deg_to_rad(360.0 / total * i)
+			split(cloned, i, total, last)
 func tryRefract():
 	if is_instance_valid(launcher) and !isChildRefract:
 		var value = launcher.fields.get(FieldStore.Entity.BULLET_REFRACTION)
@@ -159,7 +160,9 @@ func tryRefract():
 		for i in total:
 			var entity = EntityTool.findClosetEntity(position, get_tree(), !launcher.isPlayer(), launcher.isPlayer(), [launcher])
 			if is_instance_valid(entity):
-				refract(entity, i, total, last)
+				var cloned = duplicate() as BulletBase
+				cloned.look_at(entity.position)
+				refract(cloned, entity, i, total, last)
 
 # 抽象方法
 func firstFrame():
@@ -176,24 +179,10 @@ func succeedToHit(_dmg: float, _entity: EntityBase):
 	pass
 func register():
 	pass
-func split(index: int, total: int, _lastBullet: float):
-	BulletBase.generate(
-		parentScene,
-		launcher,
-		position,
-		rotation + deg_to_rad(360.0 / total * index),
-		true,
-		isChildRefract
-	)
-func refract(entity: EntityBase, _index: int, _total: int, _lastBullet: float):
-	BulletBase.generate(
-		parentScene,
-		launcher,
-		position,
-		position.angle_to_point(entity.position) if is_instance_valid(entity) else randf_range(0, deg_to_rad(360)),
-		isChildSplit,
-		true
-	)
+func split(_newBullet: BulletBase, _index: int, _total: int, _lastBullet: float):
+	pass
+func refract(_newBullet: BulletBase, _entity: EntityBase, _index: int, _total: int, _lastBullet: float):
+	pass
 
 static func generate(
 		bullet: PackedScene,
@@ -214,7 +203,6 @@ static func generate(
 		instance.isChildRefract = asChildRefract
 		instance.launcher = launchBy
 		instance.position = spawnPosition
-		instance.parentScene = bullet
 		instance.rotation = spawnRotation + deg_to_rad(launchBy.fields.get(FieldStore.Entity.OFFSET_SHOOT) * randf_range(-1, 1) * int(!ignoreOffset))
 		if addToWorld:
 			WorldManager.rootNode.call_deferred("add_child", instance)