Avoid 'comparison of unsigned expression in ‘< 0’ is always false' warning
Avoids warnings like
../Phys/SelAlgorithms/src/CombineTracksSIMD.h:66:31: warning: comparison of unsigned expression in ‘< 0’ is always false [-Wtype-limits]
66 | for ( auto i = 0ul; i < M; ++i ) { name += std::to_string( i + 3 ); }
| ~~^~~