Write integration tests with now known fail cases for master

[mathieuboudreau]

The two example cases (sphere and cylinder) that were prepared in a script (https://github.com/shimming-toolbox/susceptibility-to-fieldmap-fft/blob/main/functions/analytical_cases.py) should be moved/refactored/reused in tests.

These currently only worked for some specific settings if I recall (eg even dimensions or even padding) since there was some hardcoding,

https://github.com/shimming-toolbox/susceptibility-to-fieldmap-fft/blob/main/functions/analytical_cases.py

The integration tests should test many more cases (eg all odd, mix between even and odd) and different sizes. The phantom position could also maybe be moved?

[mathieuboudreau]

To do this, we'l have to refactor the example cases to allow for custom arguments, https://github.com/shimming-toolbox/susceptibility-to-fieldmap-fft/blob/9a60de9e478b724576d390c63070b48951df5e23/functions/analytical_cases.py#L282C1-L284C28

[mathieuboudreau]

Done in #38