Tests cubics

[SalvadorBrandolin]

Changes made:

• fixtures in tests moved to yaeos_math to organize the tests.
• Cubics implemetantion tests organized
• PR76 tests: saturation_pressure, saturation_temperature, fugacity, volume, 2 phase envelope.

[codecov[bot]]

Codecov Report

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

Project coverage is 90.70%. Comparing base (700327c) to head (5b77515). Report is 21 commits behind head on dev.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## dev #68 +/- ## ========================================== + Coverage 89.80% 90.70% +0.90% ========================================== Files 42 42 Lines 1756 1916 +160 Branches 136 137 +1 ========================================== + Hits 1577 1738 +161 Misses 110 110 + Partials 69 68 -1 ```

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[fedebenelli]

Thanks for your collaboration!