Average surface and volume derived quantities in Cylindrical and Spherical

[jhdark]

Proposed changes

With these new exports, users can take results from 1/2D simulations and extrapolate them for cylindrical and spherical cases.

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)

Further comments

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.27%. Comparing base (8d6857b) to head (10fc3b0).
Report is 37 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #820      +/-   ##
==========================================
- Coverage   99.27%   99.27%   -0.01%     
==========================================
  Files          60       60              
  Lines        2753     2744       -9     
==========================================
- Hits         2733     2724       -9     
  Misses         20       20              

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[RemDelaporteMathurin]

Here are a few comments.

On a side note, this makes me think we should try and test for cases where the surface varies in both $r$ and $z$. Like this:

[RemDelaporteMathurin]

Not true for spherical, please adapt

[RemDelaporteMathurin]

Just noting that $c$ is not equal to $c_\mathrm{right}$ with this expression (replace $r$ by $r1$)

[RemDelaporteMathurin]

I don't understand why this tests passes, please consider the above comment