Implemented ALU test cases for all operations. Added ALU testbench to active testing. Fixed bug where alu_flags module argument was defined as a 2-element logic array output rather than a 2-bit logic output

tests/tests.sv

@@ -2,4 +2,5 @@
 `include "tests/lu_tb.sv"
 `include "tests/asu_tb.sv"
 `include "tests/instruction_classifier_tb.sv"
-`include "tests/shifter_tb.sv"
+`include "tests/shifter_tb.sv"
+`include "tests/alu_tb.sv"