split traits into scalar and non-scalar part

src/tg/detail/functions/area.hh

src/tg/detail/functions/centroid.hh

src/tg/detail/functions/clamp.hh

src/tg/detail/functions/closest_points.hh

src/tg/detail/functions/cross.hh

src/tg/detail/functions/distance.hh

src/tg/detail/functions/dot.hh

src/tg/detail/functions/length.hh

src/tg/detail/functions/minmax.hh

src/tg/detail/functions/mix.hh

src/tg/detail/functions/normalize.hh

src/tg/detail/functions/project.hh

src/tg/detail/functions/round.hh

src/tg/detail/functions/uniform.hh

src/tg/detail/functions/volume.hh

src/tg/detail/macros.hh

src/tg/detail/operators/ops_pos.hh

src/tg/detail/operators/ops_size.hh

src/tg/detail/operators/ops_triangle.hh

src/tg/detail/operators/ops_vec.hh