Update memory leak test to include add_listener (#57)

Author: bghgary

Source/Windows.Test/Threading/CancellationMemoryLeakTest.cpp

@@ -10,8 +10,12 @@
 //
 // Including cancellation.h brings the no_destroy inline variable definition into
 // this translation unit, so it is constructed during static initialization before
-// main runs.  We call _CrtDumpMemoryLeaks explicitly and return a non-zero exit
-// code so that CTest treats the test as failed when leaks are detected.
+// main runs.  We also explicitly call add_listener on the none() token to verify
+// that the early-out path (which returns a dummy ticket) does not trigger any
+// heap allocations that would be reported as leaks.
+//
+// We call _CrtDumpMemoryLeaks explicitly and return a non-zero exit code so that
+// CTest treats the test as failed when leaks are detected.
 
 #include <crtdbg.h>
 #include <cstdlib>
@@ -22,6 +26,12 @@
 int main()
 {
 #ifdef _DEBUG
+    // Exercise the add_listener early-out path on cancellation::none().
+    // This should not allocate any memory since none() returns a dummy ticket.
+    {
+        auto ticket = arcana::cancellation::none().add_listener([] {});
+    }
+
     // _CrtDumpMemoryLeaks reports all CRT debug-heap blocks still allocated.
     if (_CrtDumpMemoryLeaks())
     {