Implement solution saving and exporting for refactored code

[abelsiqueira]

• Update function to compute dual
• Create function to save solution and dual values to DuckDB connection
• Update save_solution_to_file
• Update tests

Related issues

Closes #115
Closes #818

Checklist

• I am following the contributing guidelines

• Tests are passing

• Lint workflow is passing

• Docs were updated and workflow is passing

[github-actions]

Benchmark Results

	8322b5c...	838744f...	8322b5c.../838744f3abc16f...
energy_problem/create_model	31 ± 2.6 s	31.8 ± 1 s	0.977
energy_problem/input_and_constructor	16.7 ± 0.62 s	17.2 ± 0.41 s	0.973
time_to_load	4.05 ± 0.033 s	3.99 ± 0.059 s	1.02

	8322b5c...	838744f...	8322b5c.../838744f3abc16f...
energy_problem/create_model	0.311 G allocs: 15.6 GB	0.311 G allocs: 15.6 GB	1
energy_problem/input_and_constructor	0.0532 G allocs: 1.98 GB	0.0531 G allocs: 1.97 GB	1
time_to_load	0.159 k allocs: 11.2 kB	0.159 k allocs: 11.2 kB	1

Benchmark Plots

A plot of the benchmark results have been uploaded as an artifact to the workflow run for this PR.
Go to "Actions"->"Benchmark a pull request"->[the most recent run]->"Artifacts" (at the bottom).

[codecov]

Codecov Report

Attention: Patch coverage is 96.55172% with 2 lines in your changes missing coverage. Please review.

Project coverage is 95.22%. Comparing base (8322b5c) to head (838744f).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
src/solve-model.jl	95.23%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1000      +/-   ##
==========================================
- Coverage   95.43%   95.22%   -0.22%     
==========================================
  Files          29       29              
  Lines        1140     1151      +11     
==========================================
+ Hits         1088     1096       +8     
- Misses         52       55       +3     

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[datejada]

To differentiate more from the save_solution function and account for future options to export to another format, I propose renaming this function as export_solution_to_csv_files

[datejada]

Thanks for the PR @abelsiqueira; I have left some comments. Let me know what you think.

[abelsiqueira]

Thanks for the review! I've updated the PR

[datejada]

Thanks for the changes! I don´t have extra comments.