DRAFT: Fix: Double spin required since 28.2.0

This is a first attempt to fix #2589. It passes all tests,
and seems to work, but I am 90% certain it introduces unwanted
races and lost wakeups.

Anyway, its a starting point for a discussion...

rclcpp/src/rclcpp/executor.cpp

@@ -726,6 +726,25 @@ Executor::wait_for_work(std::chrono::nanoseconds timeout)
 {
   TRACETOOLS_TRACEPOINT(rclcpp_executor_wait_for_work, timeout.count());
 
+  // the real one has been added to the main waitset, therefore we need to create a copy
+  executors::ExecutorNotifyWaitable::SharedPtr notify_cpy = std::make_shared<executors::ExecutorNotifyWaitable>(*notify_waitable_);
+
+  rclcpp::WaitSet notify_only_wait_set_({}, {}, {}, {}, {}, {}, context_);
+  notify_only_wait_set_.add_waitable(notify_cpy);
+  auto res = notify_only_wait_set_.wait(std::chrono::nanoseconds(0));
+  if(res.kind() == WaitResultKind::Ready) {
+    auto & rcl_wait_set = res.get_wait_set().get_rcl_wait_set();
+    if (notify_cpy->is_ready(rcl_wait_set)) {
+      notify_cpy->execute(notify_cpy->take_data());
+
+      // As this waitable is also used to signal
+      // a cancel, we need to check it here
+      if (!spinning.load()) {
+        return;
+      }
+    }
+  }
+
   // Clear any previous wait result
   this->wait_result_.reset();