Add metallic and roughness scalar attributes to materials.

Rename `light_radius` -> `light_bulbradius`, make the default value 0.02.

PiperOrigin-RevId: 627032170
Change-Id: I1e01e2eca028c0aefc2e7dc384e8b34abac184aa

python/mujoco/structs.cc

@@ -2226,6 +2226,7 @@ This is useful for example when the MJB is not available as a file on disk.)"));
   X(headlight);
   X(directional);
   X(castshadow);
+  X(bulbradius);
 #undef X
 
 #define X(var) DefinePyArray(mjvLight, #var, &MjvLightWrapper::var)