Prepare Mod for cython

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 90.21277% with 69 lines in your changes missing coverage. Please review.

Project coverage is 87.21%. Comparing base (28eeb8f) to head (835aaf2).

Files	Patch %	Lines
pyecsca/ec/mod/flint.py	81.66%	27 Missing and 4 partials :warning:
pyecsca/ec/mod/symbolic.py	75.65%	18 Missing and 1 partial :warning:
pyecsca/ec/mod/base.py	95.34%	5 Missing and 4 partials :warning:
pyecsca/ec/transformations.py	33.34%	4 Missing :warning:
pyecsca/ec/curve.py	70.00%	3 Missing :warning:
pyecsca/ec/formula/base.py	71.43%	0 Missing and 2 partials :warning:
pyecsca/ec/params.py	75.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #67 +/- ## ========================================== + Coverage 87.13% 87.21% +0.09% ========================================== Files 86 91 +5 Lines 7706 7740 +34 Branches 1444 1447 +3 ========================================== + Hits 6714 6750 +36 Misses 703 703 + Partials 289 287 -2 ```

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