fix int overflow error for rand.Intn

[noandrea]

Closes: #5221

Description

uses instead rand.Int63n that works with
required input 1e12

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• Wrote unit and integration tests
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[codecov]

Codecov Report

Merging #5385 into master will increase coverage by 0.27%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master    #5385      +/-   ##
==========================================
+ Coverage   54.51%   54.79%   +0.27%     
==========================================
  Files         311      307       -4     
  Lines       18740    18296     -444     
==========================================
- Hits        10217    10026     -191     
+ Misses       7743     7494     -249     
+ Partials      780      776       -4

[fedekunze]

Thanks for the fix!

[alessio]

ACK from me.

Grazie Andrea!