GPU-friendly boundary representation geometry model for simulation

The SFT simulation R\&D group is working on optimizing the performance of the Geant4 particle transport simulation toolkit. This includes porting the simulation software to accelerator hardware such as graphics processing units (GPUs), which often implies major rewrites of simulation components. One of the current projects targets developing a surface-based geometry model within the VecGeom library, to mitigate the geometry performance overhead observed in GPU simulations with the current 3D-solid modeling approach. The project is in a phase where the base required functionality is implemented, but several areas are still incomplete, in particular providing surface support for the full set of supported 3D-solid primitives. This project targets extending the set of supported 3D solids to be meshed, including the unit test coverage, and integration with the GPU particle transport framework.