Handle non-uniform behaviour of __builtins__

[SimShady]

Modifications:

According to https://docs.python.org/3.9/reference/executionmodel.html:

CPython implementation detail: Users should not touch builtins; it is strictly an implementation detail. Users wanting to override values in the builtins namespace should import the builtins module and modify its attributes appropriately.

The builtins namespace associated with the execution of a code block is actually found by looking up the name builtins in its global namespace; this should be a dictionary or a module (in the latter case the module’s dictionary is used). By default, when in the main module, builtins is the built-in module builtins; when in any other module, builtins is an alias for the dictionary of the builtins module itself.

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This fix is needed to package scikit-network in nixpkgs (or at least to be able to remove the workaround)

Impacted submodules:

None

This pull request:

(your PR must match these criteria before review)

• targets the develop branch
• does not decrease code coverage
• passes the tests
• is documented and the documentation build passes (does this need documentation?)
• has PEP8-compliant code and explicit variable naming
• has a tutorial (facultative but recommended) (is this applicable for this PR?)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.62%. Comparing base (2cb2798) to head (5467ca9).
Report is 2 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #581   +/-   ##
========================================
  Coverage    97.62%   97.62%           
========================================
  Files          182      182           
  Lines         8184     8184           
========================================
  Hits          7990     7990           
  Misses         194      194           

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[mclegrand]

LGTM, thanks

[tbonald]

Thanks!