tests: intro a bench test for Array::add_all

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
lib/standard: optimize `Array::add_all`

Performances of `bench_add_all` were at 122 mIr, and after optmization
at 96 mIr.

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>