check from_string and to_string are counterparts
redesign standard value checks for this
Change-Id: I825cdba5955596096fd11ab52de571f05845d7ae
Reviewed-on: https://forge.frm2.tum.de/review/c/secop/frappy/+/34737
Tested-by: Jenkins Automated Tests <pedersen+jenkins@frm2.tum.de>
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>