simplify e_pri and e_dual computation using squared_norm properties a…

[fdtomasi]

…nd remove the use of tuples in place of higher-dimensional np.array

[codecov]

Codecov Report

Attention: Patch coverage is 92.72727% with 4 lines in your changes missing coverage. Please review.

Project coverage is 43.44%. Comparing base (4eeff4e) to head (aec1adb).
Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
regain/validation.py	63.63%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #41      +/-   ##
==========================================
+ Coverage   43.16%   43.44%   +0.28%     
==========================================
  Files          71       72       +1     
  Lines        6003     6005       +2     
==========================================
+ Hits         2591     2609      +18     
+ Misses       3412     3396      -16     

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