F.Materials -> subclass of list

[KulaginVladimir]

Proposed changes

This PR modifies F.Materials to be a subclass of list following #494.

@RemDelaporteMathurin, @jhdark, please, let me know what do you think and if this is what is needed.

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 (0353514) 98.94% compared to head (e85cf4a) 98.94%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #694   +/-   ##
=======================================
  Coverage   98.94%   98.94%           
=======================================
  Files          58       58           
  Lines        2188     2188           
=======================================
  Hits         2165     2165           
  Misses         23       23           

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[RemDelaporteMathurin]

@KulaginVladimir this is exactly what we need to do. I hope you see why it increases the readibility of the code base, and is just more logical overall.

We'd have to do the same for other classes.

A few small comments on my side

[RemDelaporteMathurin]

Looks good to me! Apologies for the back and forth discussion on equlity!

We should do the same for other classes too!