
Create a 4-bit wide, 256-to-1 multiplexer. The 256 4-bit inputs are all
packed into a single 1024-bit input vector. sel=0 should select bits
in[3:0], sel=1 selects bits in[7:4], sel=2 selects bits in[11:8], etc.

module TopModule (
  input [1023:0] in,
  input [7:0] sel,
  output [3:0] out
);

