feat(nifs): impl `protogalaxy::pow_i`

[cyphersnake]

Motivation Close #257

Overview

• Created a new module for pow_i relation calculations, calculations are done lazily, degrees are calculated once.
• protogalaxy is allocated to the module-folder

[cyphersnake]

FYI: The method is specially made so that we can use rayon::par_bridge from the outside and parralize the calculations.

However, I did not take into account that the number n may be so large that it would be difficult to store challenges at heap