Reset Visited

We actually need to traverse our grid twice - once to break the walls, then once again when we actually solve the maze (which we'll do in the next lesson).

As such, let's add a method to reset the visited property of all the cells in the maze so we can reuse it when solving the maze.

Assignment

Create a __reset_cells_visited method. It should simply reset the visited property of all the cells in the Maze to False. Call it after __break_walls_r.
Write a unit test for your method.

Run and submit the CLI tests.