feat(子弹): 为弓箭子弹添加蓄力效果和粒子特效

添加蓄力等待时间和粒子特效系统，使弓箭在发射前有蓄力效果，并在发射时显示火焰粒子特效。修改了Bow.gd和Arrow.gd以支持蓄力时间参数，并更新Arrow.tscn添加新的粒子系统节点。

scripts/Contents/Bullets/Arrow.gd

@@ -1,9 +1,23 @@
 extends BulletBase
 class_name Arrow
 
-var atk: float = 0
+@onready var trail: GPUParticles2D = $%trail
 
+var atk: float = 0
+var waitTime: float = 0
+
+func register():
+	trail.emitting = false
+	hitbox.disabled = true
 func ai():
+	if timeLived() < waitTime:
+		PresetBulletAI.lockLauncher(self, launcher, true)
+		rotation = position.angle_to_point(get_global_mouse_position())
+		position += Vector2.from_angle(rotation) * 200
+		return
+	else:
+		trail.emitting = true
+		hitbox.disabled = false
 	speed = (1 - lifeDistancePercent()) * initialSpeed
 	damage = speed * atk
 	PresetBulletAI.forward(self, rotation)

scripts/Contents/Bullets/Bow.gd

@@ -3,9 +3,9 @@ class_name Bow
 
 var count: int = 0
 var atk: float = 0
+var waitTime: float = 1000
 
 func spawn():
-	await TickTool.millseconds(1000)
 	var startAngle = rotation - deg_to_rad(count * 10.0 / 2)
 	for c in count:
 		for i in BulletBase.generate(
@@ -16,6 +16,8 @@ func spawn():
 		):
 			var bullet: Arrow = i
 			bullet.atk = atk
+			bullet.waitTime = waitTime
+	await TickTool.millseconds(waitTime)
 	tryDestroy()
 func ai():
 	PresetBulletAI.lockLauncher(self, launcher, true)