add explicit derivatives of KL shell

[rath3t]

Closes #88.

[rath3t]

@tarun-mitruka @henrij22 as an exercise can you give me a code Review. Suggest changes, more comments/doxygen comments or unclear implementations or other suggestions for refactoring.

You can wait till the CI worked

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (8837c21) 82.53% compared to head (dc4ffaf) 92.87%.

❗ Current head dc4ffaf differs from pull request most recent head 0dfe755. Consider uploading reports for the commit 0dfe755 to get more accurate results

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #225       +/-   ##
===========================================
+ Coverage   82.53%   92.87%   +10.33%     
===========================================
  Files          48       49        +1     
  Lines        1867     2022      +155     
===========================================
+ Hits         1541     1878      +337     
+ Misses        326      144      -182     

Flag	Coverage Δ
tests	92.87% <100.00%> (+10.33%)	⬆️

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[tarun-mitruka]

Hey Alex, thanks for the PR and giving for the PR review exercises. I added some comments. May be some can be incorporated in this PR and some can be moved to a new PR by opening a new issue.

[henrij22]

thanks for letting me review this PR.
I just found a few minor things, you could think about changing