Update note visuals.

rhythm_game/note/visual/hold/hold_note.gd

@@ -1,4 +1,18 @@
 class_name HoldNote extends NoteVisual
 
+@export var start: Node2D
+
+@export var end: Node2D
+
 var start_id: int
 var end_id: int
+
+func reset() -> void:
+	start_id = -1
+	end_id = -1
+
+func in_use() -> bool:
+	return start_id >= 0 or end_id >= 0
+
+func update(beat: float) -> void:
+	pass