feat(geo): Add Gen3 hierarchy search to lowestTrackingVolume (#3818)

This does not affect the existing Gen1 hierarchy search, and only kicks in when the Gen1 content is exhausted or not present at all. This is not optimal with many volumes, and I plan to develop a mechanism to implement volume local accelerated search.

Part of #3502

Core/src/Geometry/TrackingVolume.cpp

@@ -96,6 +96,13 @@ const TrackingVolume* TrackingVolume::lowestTrackingVolume(
     }
   }
 
+  // @TODO: Abstract this into an accelerateable structure
+  for (const auto& volume : volumes()) {
+    if (volume.inside(position, tol)) {
+      return volume.lowestTrackingVolume(gctx, position, tol);
+    }
+  }
+
   // there is no lower sub structure
   return this;
 }