Add scenes, static scene-finding mechanism, and scene pool for visual hold/tap notes.

rhythm_game/note/visual/note_animator.gd

@@ -0,0 +1,27 @@
+class_name NoteAnimator extends NoteView
+
+@export var pool: NotePool
+
+## TODO WARNING: This is currently only implemented for beat updates
+## going forward in time.
+func update_current_beat(beat: float) -> void:
+	var old_begin: int = _begin
+	var old_end: int = _end
+	super.update_current_beat(beat) # Update _begin and _end.
+	_update_note_visuals(old_begin, _begin)
+	_update_note_visuals(old_end, _end)
+
+
+# ======== IMPLEMENTATION ======== #
+var _note_map: Dictionary[int, NoteVisual]
+
+func _update_note_visuals(index_begin: int, index_end: int) -> void:
+	for i: int in range(index_begin, index_end):
+		# TODO: Either get or return node from pool,
+		# depending on if index_begin > or < than index_end.
+		pass
+
+func _set_notes(p_notes: NoteArray) -> void:
+	
+	notes = p_notes
+	_reset_view()