Add neutronics documentation and vault image

[davidepettinari]

This PR adds detailed documentation on the neutronics model and includes a vault image for better visualization.

Changes:

• Added documentation covering the neutronics model, including material composition and geometry details.
• Included an image of the vault to enhance clarity in the documentation.
• Specified that the model's origin point (0.0, 0.0, 0.0) is located at the bottom right corner when entering the vault room.

[RemDelaporteMathurin]

https://libra-toolbox--53.org.readthedocs.build/en/53/modules/libra_toolbox.neutronics.html

Hm for some reason the neutronics module page is empty... I'll try to fix this when I find time

[RemDelaporteMathurin]

Do not track this file in version control

Avoid using git add .

[RemDelaporteMathurin]

@davidepettinari it seems like pandas it required to build the docs (see this error in the build). Can you add pandas as a requirement in the requirements.txt file?

[codecov]

Codecov Report

❌ Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.37%. Comparing base (2569f9b) to head (9746eb6).

Files with missing lines	Patch %	Lines
libra_toolbox/_version.py	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #53      +/-   ##
==========================================
- Coverage   87.11%   86.37%   -0.75%     
==========================================
  Files          19       20       +1     
  Lines        1506     1519      +13     
==========================================
  Hits         1312     1312              
- Misses        194      207      +13     

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