fix: using 2^256 for the vrf denominator

[b00f]

Description

Updating denominator fro the VRF to 2^256.

Checklist

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• My code follows the code style of this project.
• I have added tests to cover my changes.
• All new and existing tests passed.
• CHANGELOG is updated.

[codecov]

Codecov Report

Merging #445 (84f5043) into main (a8c6be9) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #445      +/-   ##
==========================================
+ Coverage   82.15%   82.17%   +0.02%     
==========================================
  Files         148      148              
  Lines        6947     6945       -2     
==========================================
  Hits         5707     5707              
+ Misses        950      949       -1     
+ Partials      290      289       -1