Refactor some of the code related to model creation

[abelsiqueira]

• Create new files src/utils.jl and src/model-preparation.jl to help split the code from src/create-model.jl.
• The file src/utils.jl contains useful functions for create_model.
• The file src/model-preparation should be useful in the future for data and structure creation that should happen before the model.
• Create a simple sets NamedTuple for this section.
• Create function add_expressions_to_dataframe! with a large chunk of code from create_model that adds incoming and outgoing flows to some dataframes.
• Create function create_variables! that creates the variables in create_model.
• Both of these functions actually involve things happening inside create_model, but for now we are keeping them there.

---

• Move the sets creation to a function create_sets.
• Store the sets in a NamedTuple

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.90%. Comparing base (fc68311) to head (090b109).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #886   +/-   ##
=======================================
  Coverage   99.90%   99.90%           
=======================================
  Files          20       22    +2     
  Lines        1023     1046   +23     
=======================================
+ Hits         1022     1045   +23     
  Misses          1        1           

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[github-actions]

Benchmark Results

	fc68311...	090b109...	fc68311.../090b10958c37e2...
energy_problem/create_model	42.9 ± 1.9 s	45.9 ± 1.1 s	0.936
energy_problem/input_and_constructor	8.75 ± 0.41 s	8.82 ± 0.4 s	0.992
time_to_load	4.04 ± 0.036 s	4.05 ± 0.027 s	0.997

	fc68311...	090b109...	fc68311.../090b10958c37e2...
energy_problem/create_model	0.645 G allocs: 22.5 GB	0.645 G allocs: 22.5 GB	1
energy_problem/input_and_constructor	9.53 M allocs: 0.695 GB	9.53 M allocs: 0.695 GB	1
time_to_load	0.157 k allocs: 11.1 kB	0.157 k allocs: 11.1 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).

[abelsiqueira]

Copy-pasted from previous run comparing only the first commit

	fc68311...	ea4291f...	fc68311.../ea4291f8d9269b...
energy_problem/create_model	46.8 ± 1.6 s	49.5 ± 1.9 s	0.947
energy_problem/input_and_constructor	9.27 ± 0.59 s	9.78 ± 0.34 s	0.947
time_to_load	4.31 ± 0.018 s	4.31 ± 0.073 s	1

	fc68311...	ea4291f...	fc68311.../ea4291f8d9269b...
energy_problem/create_model	0.645 G allocs: 22.5 GB	0.645 G allocs: 22.5 GB	1
energy_problem/input_and_constructor	9.53 M allocs: 0.695 GB	9.53 M allocs: 0.695 GB	1
time_to_load	0.157 k allocs: 11.1 kB	0.157 k allocs: 11.1 kB	1

[abelsiqueira]

This doesn't close #885, but it can be merged

[datejada]

LGTM. Thanks!