[multimod] Improve error message when Go proxy misbehaves

[mx-psi]

• Check status code of reply from Go proxy and fail if status code is 4xx or 5xx.
• Add information about package and tag that caused the failure

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 53.10%. Comparing base (06a3912) to head (be1f84f).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #610      +/-   ##
==========================================
+ Coverage   53.03%   53.10%   +0.06%     
==========================================
  Files          51       51              
  Lines        2255     2258       +3     
==========================================
+ Hits         1196     1199       +3     
  Misses        912      912              
  Partials      147      147              

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