DiffusionPWLCSolver(std::string text_name, const chi_math::SpatialDiscretization &sdm, const chi_math::UnknownManager &uk_man, std::map< uint64_t, BoundaryCondition > bcs, MatID2XSMap map_mat_id_2_xs, const std::vector< UnitCellMatrices > &unit_cell_matrices, bool verbose)