Add minimum node state constraint

[datejada]

This pull request introduces a new constraint, constraint_min_node_state, to ensure a minimum storage content for nodes in the SpineOpt model. It includes updates to the codebase, documentation, and tests to support this new functionality. Below are the most important changes grouped by theme:

New Constraint Implementation:

• Added the constraint_min_node_state implementation in src/constraints/constraint_min_node_state.jl, including the constraint logic, indices, and helper functions. This ensures that the node_state variable meets a minimum threshold based on storage capacity and node_state_min.

Integration into SpineOpt Workflow:

• Included the new constraint file constraint_min_node_state.jl in src/SpineOpt.jl.
• Updated function _add_constraints! in src/run_spineopt_basic.jl to add the new constraint during the model-building process.

Data Preprocessing:

• Added a new function, generate_node_state_lower_limit, in src/data_structure/preprocess_data_structure.jl to compute the lower limit for node_state based on input parameters.
• Updated the preprocessing pipeline in function preprocess_data_structure to include the generation of node_state_lower_limit.

Variable Updates:

• Modified function add_variable_node_state! in src/variables/variable_node_state.jl to use the new lower bound function node_state_lb for the node_state variable.
• Introduced node_state_lb in src/variables/variable_node_state.jl to calculate the lower bound for node_state.

Testing:

• Added a new test, test_constraint_min_node_state_investments, in test/constraints/constraint_node.jl to validate the behavior of the new constraint.
• Integrated the new test into the overall test suite.

Documentation:

• Documented the new constraint in docs/src/mathematical_formulation/constraints.md under the "Minimum node state" section.

Fixes #1200

Checklist before merging

• Documentation is up-to-date
• Unit tests have been added/updated accordingly
• Code has been formatted according to SpineOpt's style
• Unit tests pass

[Copilot]

Pull Request Overview

This PR adds a new constraint to ensure a minimum storage content for nodes in the SpineOpt model. Key changes include the addition of the constraint_min_node_state, its integration into the SpineOpt workflow, and updates to data preprocessing, variable bounds, testing, and documentation.

Files not reviewed (6)

• src/SpineOpt.jl: Language not supported
• src/constraints/constraint_min_node_state.jl: Language not supported
• src/data_structure/preprocess_data_structure.jl: Language not supported
• src/run_spineopt_basic.jl: Language not supported
• src/variables/variable_node_state.jl: Language not supported
• test/constraints/constraint_node.jl: Language not supported

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.39%. Comparing base (fa66a48) to head (1dda716).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1204      +/-   ##
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+ Coverage   87.35%   87.39%   +0.04%     
==========================================
  Files         144      145       +1     
  Lines        4451     4466      +15     
==========================================
+ Hits         3888     3903      +15     
  Misses        563      563              

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