fix: async registerNanoContract call

[tuliomir]

We were having intermittent failures on the CI ( example ) due to a NanoContract registration promise being out of sync with the flow of the test suite. This PR ensures they stay in sync by returning the lower level promise instead of just firing it.

This is a similar solution as the one applied on 641.

Acceptance Criteria

• The registerNanoContract method should return its underlying operation Promise<void>

Security Checklist

• Make sure you do not include new dependencies in the project unless strictly necessary and do not include dev-dependencies as production ones. More dependencies increase the possibility of one of them being hijacked and affecting us.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.48%. Comparing base (2892428) to head (6674f28).

Additional details and impacted files

@@             Coverage Diff             @@
##           master     #646       +/-   ##
===========================================
+ Coverage   62.01%   79.48%   +17.47%     
===========================================
  Files          77       77               
  Lines        5826     5826               
  Branches     1210     1223       +13     
===========================================
+ Hits         3613     4631     +1018     
+ Misses       2116     1178      -938     
+ Partials       97       17       -80     

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