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]

Codecov Report

All modified and coverable lines are covered by tests ✅

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

Additional details and impacted files

@@            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!