Soret coefficient as a function of temperature

[KulaginVladimir]

This PR makes it possible to set the Soret coefficient as a function of temperature, according to #458. Following the discussion, the parameter is renamed to Q and expressed in eV. Most of the changes are made based on #468.

Basic usage:

from FESTIM import Material

my_mat = Material(id=1, D_0=1, E_D=0, Q=lambda T: 2 + 5 * T)
# or
my_mat = Material(id=1, D_0=1, E_D=0, Q=10)

Types of changes

What types of changes does your code introduce to FESTIM?

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Code refactoring
• Documentation Update (if none of the other choices apply)
• New tests

Checklist

• Black formatted
• Unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (2ae06c1) 98.95% compared to head (ada717a) 98.94%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #690      +/-   ##
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- Coverage   98.95%   98.94%   -0.01%     
==========================================
  Files          58       58              
  Lines        2195     2181      -14     
==========================================
- Hits         2172     2158      -14     
  Misses         23       23              

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[jhdark]

@mougenj Its finally coming!

[RemDelaporteMathurin]

Thanks for this PR @KulaginVladimir , just a small comment on the docstrings, we could add an example of using a lambda function.

Also, do we have an MMS test for the soret effect? I don't know if we tested it thoroughly or not. Can be done in a separate PR if we don't

[RemDelaporteMathurin]

Thanks @KulaginVladimir 🚀 I'll leave this open to leave others the time to make some comments if needed.