convert pdf_norm and cdf_norm to pure while improving scale check (#679)

* convert proc to pure, comment out scale check

* switch back rvs_norm to impure

zigset changes global parameters and thus can't be pure

* remove comments and prettify

* added protection against scale<=0

* fix nan implementation

* add ieee_value

* fprettify -i 4

---------

Co-authored-by: milancurcic <[email protected]>

Author: HugoMVale