Update nixpkgs & build caching with nix

[hellwolf]

[github-actions[bot]]

Changelog Reminder

Reminder to update the CHANGELOG.md for any of the modified packages in this PR.

• [ ] CHANGELOG.md modified
• [ ] Double check before merge

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 88.44%. Comparing base (23b300d) to head (c909db5). Report is 1 commits behind head on dev.

Additional details and impacted files

@@           Coverage Diff           @@
##              dev    #1929   +/-   ##
=======================================
  Coverage   88.44%   88.44%           
=======================================
  Files         111      111           
  Lines        6964     6964           
  Branches      933      934    +1     
=======================================
  Hits         6159     6159           
  Misses        803      803           
  Partials        2        2           

Flag	Coverage Δ
ethereum-contracts	94.50% <ø> (ø)
sdk-core	88.44% <ø> (ø)

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[hellwolf]

Now it takes around 1 minutes to restore the cached workflow result.

[hellwolf]

An example of cached workflow:

[github-actions[bot]]

XKCD Comic Relif

Link: https://xkcd.com/1929