graph: move light level calculation to thread worker

fix: nodes with light level 0.0 should trigger bots flashlight now
fix: gcc and msvc builds due to mistake in crlib
refactor: add more const-correctness (ongoing)

inc/graph.h

@@ -228,6 +228,7 @@ public:
    void reset ();
    void frame ();
    void populateNodes ();
+   void syncInitLightLevels ();
    void initLightLevels ();
    void initNarrowPlaces ();
    void addPath (int addIndex, int pathIndex, float distance);