Upgrade onflow/crypto and clarify build details

[tarakby]

• upgrade onflow/crypto
• clarify build constraints related to https://github.com/onflow/crypto when importing the flow-go module. This also addresses Update docs: clarify library usage crypto#7.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 55.66%. Comparing base (51a3fb6) to head (7c4af2d).
Report is 113 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5601      +/-   ##
==========================================
- Coverage   55.67%   55.66%   -0.02%     
==========================================
  Files        1037     1041       +4     
  Lines      101404   101935     +531     
==========================================
+ Hits        56457    56742     +285     
- Misses      40607    40840     +233     
- Partials     4340     4353      +13     

Flag	Coverage Δ
unittests	55.66% <ø> (-0.02%)	⬇️

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