Implementation of the GERG2008 EoS using hyperdual numbers

[fedebenelli]

While on the long we'll implement analytic derivatives, this will suffice for a lot of use cases.

The principal parts of this implementation are:

• GERG2008 derived type that handle the EoS and uses two derived types to hold the parameters:
  • GERG2008Pure derived type that keeps the pure components parameters.
  • GERG2008Binary derived type that keeps the binary parameters.
  • G2008Components enum, which helps identifying the ids of each components

There is also the gerg_2008 function that sets the parameters based on the ids, using the default parameters from the paper.

[codecov]

Codecov Report

Attention: Patch coverage is 99.81818% with 3 lines in your changes missing coverage. Please review.

Project coverage is 92.64%. Comparing base (c3e66dd) to head (82fe4f1).
Report is 7 commits behind head on dev.

Files with missing lines	Patch %	Lines
src/models/models.f90	0.00%	1 Missing ⚠️
.../models/residual_helmholtz/multifluid/gerg2008.f90	98.66%	1 Missing ⚠️
...idual_helmholtz/multifluid/parameters_gerg2008.f90	99.93%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #133      +/-   ##
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+ Coverage   89.61%   92.64%   +3.02%     
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  Files          77       81       +4     
  Lines        4296     5940    +1644     
  Branches      298      300       +2     
==========================================
+ Hits         3850     5503    +1653     
+ Misses        371      362       -9     
  Partials       75       75              

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