Drop matplotlib dependency

[alecandido]

matplotlib seems unused in qibo, and only used in the examples

• src: https://github.com/search?q=repo%3Aqiboteam%2Fqibo+%2F%5Cbmatplotlib%2F+path%3Asrc%2F&type=code
• examples: https://github.com/search?q=repo%3Aqiboteam%2Fqibo+%2F%5Cbmatplotlib%2F+path%3Aexamples%2F&type=code

#814

Checklist:

• Reviewers confirm new code works as expected.
• Tests are passing.
• Coverage does not decrease.
• Documentation is updated.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (1dd73f7) 100.00% compared to head (84bc7e3) 100.00%.

Additional details and impacted files

@@            Coverage Diff            @@
##            master     #1120   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files           65        65           
  Lines         9059      9059           
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  Hits          9059      9059           

Flag	Coverage Δ
unittests	100.00% <ø> (ø)

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[stavros11]

Thanks. Out of curiosity, shouldn't we add matplotlib somewhere as optional? I think there are some tests for the examples in CI, but they are still passing so I guess it was installed as a dependecy of another dependency?

[scarrazza]

Dropping is fine but I agree with @stavros11 that we should add it as optional.

[alecandido]

Thanks. Out of curiosity, shouldn't we add matplotlib somewhere as optional? I think there are some tests for the examples in CI, but they are still passing so I guess it was installed as a dependecy of another dependency?

I don't believe it should be optional, but rather it should be in the tests group.

The spirit is that:

• optional dependencies are runtime dependencies, that might be needed by the user to execute some library functions, that are not part of the main workflow
• groups are development dependencies, so they are used by developers but not by users (so they do not survive in the package)

Of course, a Qibo user might want to use matplotlib for something else. But that's completely independent of Qibo.

[scarrazza]

Fine by me in the tests group. We could also add a sentence in the examples/README.md that some example require matplotlib.