feat(子弹): 为VectorStar添加分裂逻辑并重构ArrowSeven

为VectorStar子弹添加分裂时的特殊处理逻辑，确保分裂出的新子弹不会被标记为forwarded
将ArrowSeven子弹重命名为ArrowSevenBullet以明确类名，并移除多余空行

scripts/Contents/Bullets/VectorStar.gd

@@ -16,3 +16,6 @@ func ai():
 		speed = (timeLived() - forwardTime) / 30
 		if is_instance_valid(tracer):
 			rotation = position.angle_to_point(tracer.getTrackingAnchor())
+func split(newBullet: BulletBase, _index: int, _total: int, _lastBullet: float):
+	if newBullet is VectorStar:
+		newBullet.forwarded = false