Improve frozen code

freeze.lua

@@ -3,13 +3,13 @@ function classroom.is_frozen(player)
 end
 
 minetest.register_entity("classroom:freeze", {
+	-- This entity needs to be visible otherwise the frozen player won't be visible.
 	initial_properties = {
-		physical = true,
-		collisionbox = { -0.01, -0.01, -0.01, 0.01, 0.01, 0.01 },
 		visual = "sprite",
 		visual_size = { x = 0, y = 0 },
 		textures = { "blank.png" },
-		is_visible = true,
+		physical = false, -- Disable collision
+		pointable = false, -- Disable selection box
 		makes_footstep_sound = false,
 	},