Use subtle From<Choice> for bool impl instead of using unwrap_u8

[brycx]

This should avoid potential short-circuits. Using unwrap_u8 was completely useless here.

[codecov]

Codecov Report

Merging #66 into master will decrease coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #66      +/-   ##
==========================================
- Coverage   96.39%   96.37%   -0.02%     
==========================================
  Files          47       47              
  Lines        6656     6655       -1     
==========================================
- Hits         6416     6414       -2     
- Misses        240      241       +1

Impacted Files	Coverage Δ
src/util/mod.rs	100% <100%> (ø)	⬆️
src/typedefs.rs	97.87% <100%> (-0.01%)	⬇️
src/hazardous/xof/cshake.rs	97.69% <0%> (-0.39%)	⬇️

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