Allow mesh material volume calculations outside model geometry

[paulromano]

Description

Updates Mesh.material_volumes to support meshes that extend beyond the model geometry. During ray tracing, regions outside the geometry are simply treated as void material. This enables a user to, for example, use Cartesian meshes to cover geometries with a curved outside boundary (sphere, cylinder). The implementation follows the ray-traced plotting approach for locating model boundaries from undefined space (utilizing advance_to_boundary_from_void). Tests have been updated, including a comparison against an equivalent geometry with an explicit enclosing void cell.

Checklist

• I have performed a self-review of my own code
• I have run clang-format (version 18) on any C++ source files (if applicable)
• I have followed the style guidelines for Python source files (if applicable)
• I have made corresponding changes to the documentation (if applicable)
• I have added tests that prove my fix is effective or that my feature works (if applicable)