feat(L04): add RV32I decoder and register file card

tests/task01_instruction_fields_tb.sv

@@ -0,0 +1,17 @@
+module tb;
+    logic [31:0] instr;
+    logic [6:0] opcode, funct7;
+    logic [4:0] rd, rs1, rs2;
+    logic [2:0] funct3;
+    logic signed [31:0] imm_i;
+    string trace_file;
+    instruction_fields dut (.*);
+    initial begin
+        if ($value$plusargs("trace=%s", trace_file)) begin $dumpfile(trace_file); $dumpvars(0, tb); end
+        instr = 32'hffc30293; #1;
+        if (opcode != 7'h13 || rd != 5 || rs1 != 6 || funct3 != 0 || $signed(imm_i) != -4)
+            $fatal(1, "FAIL task01 opcode=%h rd=%0d rs1=%0d imm=%0d", opcode, rd, rs1, $signed(imm_i));
+        $display("PASS task01 instr=ffc30293 opcode=13 rd=5 rs1=6 funct3=0 imm=-4");
+        $finish;
+    end
+endmodule