Add global scroll speed setting.

rhythm_game/settings.gd

@@ -0,0 +1,9 @@
+@abstract class_name Settings extends Object
+
+## World coordinate units (pixels) per beat.
+static func get_note_scroll_speed() -> float:
+	return _note_scroll_speed
+
+
+# ======== IMPLEMENTATION ======== #
+static var _note_scroll_speed: float = 20.0

rhythm_game/settings.gd.uid

@@ -0,0 +1 @@
+uid://k0no5veq8xco