Increase calorimeter size by 4x in every dimension

Scales the default transverse width (xywidth 50->200 cm) and every
layer thickness across the example/production geometries (run_pbwo4,
example.py/ipynb, run_sampling configs, export_xsec) by the same
factor, so the calo grows uniformly in x, y, and z.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

include/GeometryDescriptor.hh

@@ -134,7 +134,7 @@ public:
 
 class GeometryDescriptor {
 public:
-    GeometryDescriptor() : xywidth(50), g4system(nullptr) {};
+    GeometryDescriptor() : xywidth(200), g4system(nullptr) {};
     ~GeometryDescriptor();
 
     void addLayer(double thickness_cm, std::string material, bool isActive = true, int nx = 1, int ny = -1);