test: improve functional tests

[mkniewallner]

PR Checklist

• A description of the changes is added to the description of this PR.
• If there is a related issue, make sure it is linked to this PR.
• If you've fixed a bug or added code that should be tested, add tests!
• If you've added or modified a feature, documentation in docs is updated

Description of changes

Bunch of improvements on functional tests, the main one being that we now depend on exact versions for dependencies, to improve a bit build reproducibility. Windows PyPy 3.10 have been randomly failing, so if we are lucky, this might help on that front.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.6%. Comparing base (b8e1882) to head (960be45).
Report is 1 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main    #921   +/-   ##
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  Coverage   92.6%   92.6%           
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  Files         37      37           
  Lines       1006    1006           
  Branches      99      99           
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  Hits         932     932           
  Misses        59      59           
  Partials      15      15           

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[mkniewallner]

Merging this one because I have the feeling this could solve the failing Windows PyPy 3.10 tests, and I'm tired of the failure 😄