feat(L03): add blinker and synchronous logic card

tests/task01_clock_enable_tb.sv

@@ -0,0 +1,33 @@
+module tb;
+    logic clk = 0;
+    logic rst = 1;
+    logic enable;
+    logic [1:0] count;
+    integer pulses = 0;
+    integer consecutive = 0;
+    logic previous = 0;
+    string trace_file;
+
+    clock_enable dut (.*);
+    always #1 clk = ~clk;
+
+    initial begin
+        if ($value$plusargs("trace=%s", trace_file)) begin
+            $dumpfile(trace_file);
+            $dumpvars(0, tb);
+        end
+        repeat (2) @(posedge clk);
+        @(negedge clk);
+        rst = 0;
+        repeat (16) begin
+            @(posedge clk); #1;
+            if (enable) pulses += 1;
+            if (enable && previous) consecutive += 1;
+            previous = enable;
+        end
+        if (pulses != 4 || consecutive != 0 || count != 0)
+            $fatal(1, "FAIL task01 pulses=%0d consecutive=%0d count=%0d", pulses, consecutive, count);
+        $display("PASS task01 pulses=4 consecutive=0 final_count=0");
+        $finish;
+    end
+endmodule