[TEST] Adds support of cython for pytest

[skoudoro]

This PR fixes #2719.

The goal is to allow Pytest to run test on *.pyx files and especially cdef function.

Currently, our cedf function are not tested which is quite problematic.

@gabknight, you will be interested to this PR. Also, the cross is failing, Can you look into it a create a new PR to fix it?

Thanks!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (fb4005f) 82.39% compared to head (50afd80) 82.38%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3048      +/-   ##
==========================================
- Coverage   82.39%   82.38%   -0.01%     
==========================================
  Files         146      145       -1     
  Lines       20631    20624       -7     
  Branches     3319     3319              
==========================================
- Hits        16999    16992       -7     
  Misses       2802     2802              
  Partials      830      830              

see 1 file with indirect coverage changes

[skoudoro]

You can see on the CI new tests for pyx files : https://github.com/dipy/dipy/actions/runs/7659584839/job/20875012290?pr=3048#step:9:3779

[gabknight]

Looks good. In my environment, the test test_cross() passes. Could you share the error you are getting.