input: Write a python function to instantiate a BoardGame object and play turns until the game ends.
  assert play_game(BoardGame(2, 5)) is not None
  assert play_game(BoardGame(4, 10)) is not None
  assert play_game(BoardGame(3, 7)) is not None
output: def play_game(game):
      while not game.is_game_over():
          for player in range(game.num_players):
              game.play_turn(player)
              if game.is_game_over():
                  break
      return game