Implement lane update.

rhythm_game/lane/lane.gd

@@ -6,4 +6,5 @@ func get_hit_pos() -> Vector2:
 
 ## Should be connected to [signal NoteSpawner.notes_spawned].
 func update(beat: float) -> void:
-	pass
+	for note: NoteVisual in get_children():
+		note.update(beat)