(feat) refactor tests with fixture

[MementoRC]

The purpose is to be able to run pytest with the cibuildwheel feature. cibuildwheel install the tests in a manner that prevent tests to be recognized as a package and thus there is pretty much no way to import samples (at least none within the 50 commits I made on my branch to test it out!)

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 85.68%. Comparing base (b8e9dfe) to head (746f7c9).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #146 +/- ## ========================================== + Coverage 85.63% 85.68% +0.05% ========================================== Files 11 11 Lines 564 566 +2 Branches 66 67 +1 ========================================== + Hits 483 485 +2 Misses 45 45 Partials 36 36 ``` | [Files](https://app.codecov.io/gh/ofek/coincurve/pull/146?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Ofek+Lev) | Coverage Δ | | |---|---|---| | [tests/conftest.py](https://app.codecov.io/gh/ofek/coincurve/pull/146?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Ofek+Lev#diff-dGVzdHMvY29uZnRlc3QucHk=) | `100.00% <100.00%> (ø)` | | | [tests/test\_ecdsa.py](https://app.codecov.io/gh/ofek/coincurve/pull/146?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Ofek+Lev#diff-dGVzdHMvdGVzdF9lY2RzYS5weQ==) | `100.00% <100.00%> (ø)` | | | [tests/test\_keys.py](https://app.codecov.io/gh/ofek/coincurve/pull/146?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Ofek+Lev#diff-dGVzdHMvdGVzdF9rZXlzLnB5) | `100.00% <100.00%> (ø)` | | | [tests/test\_utils.py](https://app.codecov.io/gh/ofek/coincurve/pull/146?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Ofek+Lev#diff-dGVzdHMvdGVzdF91dGlscy5weQ==) | `100.00% <100.00%> (ø)` | |

[ofek]

Which should I review first?

[MementoRC]

This PR and safer download are fairly independent and already incorporated to the third one, they should be fairly straightforward to review and mostly come down to whether you want to go that direction or not,

I may add more smaller ones to carve out the bigger one, I was working on it and saw that you started to be active, so i wanted to tickle your attention

[MementoRC]

This should help enable the full pytest test-suite for the built the wheels with cibuildwheel