Remove hex package dependency

[nogringo]

No description provided.

[1-leo]

very nice!

[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 71.06%. Comparing base (55fd631) to head (0aafe96).
⚠️ Report is 7 commits behind head on master.

Files with missing lines	Patch %	Lines
packages/ndk/lib/shared/nips/nip01/helpers.dart	66.66%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #294   +/-   ##
=======================================
  Coverage   71.06%   71.06%           
=======================================
  Files         136      136           
  Lines        4766     4766           
=======================================
  Hits         3387     3387           
  Misses       1379     1379           

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