Rename tb sum→result to avoid duplicate waveform signal names

The VCD dumper records both the tb-level wire and the dut port by name.
When both are called 'sum' it looks like a confusing duplicate; renaming
the tb wire to 'result' makes the two hierarchy levels distinct.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: thomasahle

src/lessons/sv/modules-and-ports/tb.sv

@@ -1,11 +1,12 @@
 module tb;
-  logic [7:0] a, b, sum;  // stimulus signals
+  logic [7:0] a, b;
+  logic [7:0] result;            // tb-level wire to capture the output
 
   // Instantiate the design under test, connecting ports by name
-  adder dut(.a(a), .b(b), .sum(sum));
+  adder dut(.a(a), .b(b), .sum(result));
 
   initial begin
-    a = 8'd10; b = 8'd32;       // apply inputs
-    #1 $display("sum = %0d", sum); // wait 1 time unit, then print result
+    a = 8'd10; b = 8'd32;              // apply inputs
+    #1 $display("sum = %0d", result);  // wait 1 time unit, then print result
   end
 endmodule