🎨 Restructured sidb_charge_state and added tests

[marcelwa]

Description

This PR adds tests for the functions associated with sidb_charge_state and restructures the respective header a bit.

Checklist:

• The pull request only contains commits that are related to it.
• I have added appropriate tests and documentation.
• I have made sure that all CI jobs on GitHub pass.
• The pull request introduces no new warnings and follows the project's style guidelines.

[codecov]

Codecov Report

Merging #168 (72b0128) into main (acbe7aa) will increase coverage by 0.00%.
The diff coverage is 100.00%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #168   +/-   ##
=======================================
  Coverage   94.24%   94.24%           
=======================================
  Files          76       76           
  Lines        7070     7088   +18     
=======================================
+ Hits         6663     6680   +17     
- Misses        407      408    +1     

Impacted Files	Coverage Δ
.../fiction/algorithms/iter/aspect_ratio_iterator.hpp	100.00% <ø> (ø)
...n/algorithms/verification/equivalence_checking.hpp	89.79% <ø> (ø)
include/fiction/technology/sidb_charge_state.hpp	91.89% <100.00%> (+2.41%)	⬆️

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[github-actions]

clang-tidy review says "All clean, LGTM! 👍"