Add unit tests for chain syncing (#87)

src/scanner.h

@@ -56,5 +56,8 @@ namespace lws
 
     //! Stops all scanner instances globally.
     static void stop() noexcept { running = false; }
+
+    //! For testing, \post is_running() == true
+    static void reset() noexcept { running = true; }
   };
 } // lws