feat(cmat): pass hints to Ex42 observers

Extend the Ex42 observer pattern with Hint objects so each
observer receives the reason for the update instead of
querying the subject:

- Subject::notify() and Observer::update() now take a
  const Hint& argument.
- Add LightHint and WaitHint carrying the traffic light
  state and WAIT button state, defined in Pelican.h.
- Pole dispatches on hint type using dynamic_cast.
- The Pole constructor sets its initial lights directly
  from the Pelican's current state, since no notification
  is sent at startup. Stopgap until the initial update
  is handled properly.

Co-authored-by: Qwen 3.8 27B <qwen3.8_27b-q3_k_xl@lmstudio.local>

cmat/Ex42/Subject.cpp

@@ -1,12 +1,12 @@
-
-
-#include "Subject.h"
-#include "Observer.h"
-
-void Subject::attach(Observer &obs) { myObservers.insert(&obs); }
-
-void Subject::notify() const {
-    for (ObsList::const_iterator iter = myObservers.begin(); iter != myObservers.end(); ++iter) {
-        (*iter)->update();
-    }
-}
+
+
+#include "Subject.h"
+#include "Observer.h"
+
+void Subject::attach(Observer &obs) { myObservers.insert(&obs); }
+
+void Subject::notify(const Hint& hint) const {
+    for (ObsList::const_iterator iter = myObservers.begin(); iter != myObservers.end(); ++iter) {
+        (*iter)->update(hint);
+    }
+}