In a seven-segment LED display, a square pattern can be created
by enabling the a, b, f, and g segments or the c, d, e, and g
segments. We want to design a circuit that circulates the square
patterns in the four-digit seven-segment LED display. The circuit
should have an input, en, which enables the circulation, and an
input, cw, which specifies the direction (i.e., clockwise or
counterclockwise) of the circulation. Write in verilog please.