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

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Co-authored-by: milancurcic <caomaco@gmail.com>

Author: HugoMVale