Isolate integer and bits gadgets out of the traits::utilities module

[howardwu]

Motivation

Isolate integer and bits gadgets out of the traits::utilities module

[codecov]

Codecov Report

Merging #186 (b38927f) into feat/ergonomics (4600a4a) will increase coverage by 0.03%.
The diff coverage is n/a.

❗ Current head b38927f differs from pull request most recent head e001c6c. Consider uploading reports for the commit e001c6c to get more accurate results

@@                 Coverage Diff                 @@
##           feat/ergonomics     #186      +/-   ##
===================================================
+ Coverage            92.94%   92.98%   +0.03%     
===================================================
  Files                   61       61              
  Lines                 2666     2666              
===================================================
+ Hits                  2478     2479       +1     
+ Misses                 188      187       -1     

Impacted Files	Coverage Δ
curves/src/edwards_bls12/tests.rs	83.22% <0.00%> (+0.64%)	⬆️

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