fix broken sudoku example

[guglielmosanchini]

• x = model.binary_var_dict(idx, "X") must be x = model.binary_var_dict(idx, name="X"), otherwise "X" is interpreted as lower bound;
• solution.print_information() does not exist, should be model.solve_details.print_information();
• The constraint about the 3x3 sectors containing each number only once was missing.