Added testbench for instruction classifier and fixed compilation errors. Should be fine to synthesise but icarus does not like the constant bit extraction in the always_comb block for some reason.

tests/tests.sv

@@ -1,3 +1,4 @@
 `include "tests/seven_seg_tb.sv"
 `include "tests/lu_tb.sv"
-`include "tests/asu_tb.sv"
+`include "tests/asu_tb.sv"
+`include "tests/instruction_classifier_tb.sv"