Add GetProblem method to Solution interface for retrieving optimization problems

[Copilot]

Overview

This PR implements the GetProblem method for the solution.Solution interface as requested in issue #22. This method allows solutions to maintain and retrieve a reference to the optimization problem they solve.

Changes

Interface Enhancement

Added GetProblem() *problem.OptimizationProblem method to the Solution interface in solution/solution.go. This method returns a pointer to the optimization problem that the solution is associated with.

DummySolution Implementation

• Added a Problem field to the DummySolution struct to store the optimization problem reference
• Implemented the GetProblem() method that returns the stored problem

Testing

Added comprehensive tests in testing/solution/solution_test.go:

• TestSolution_GetProblem1: Verifies that a solution can correctly retrieve its associated problem
• TestSolution_GetProblem2: Verifies that GetProblem returns nil when no problem is set

Usage Example

// Create an optimization problem
p := problem.NewProblem("MyOptimizationProblem")
v1 := p.AddVariable()

// Create a solution associated with the problem
sol := solution.DummySolution{
    Values: map[uint64]float64{
        v1.ID: 2.5,
    },
    Objective: 10.0,
    Status:    solution_status.OPTIMAL,
    Problem:   p,
}

// Retrieve the problem from the solution
retrievedProblem := sol.GetProblem()
fmt.Println(retrievedProblem.Name) // Output: "MyOptimizationProblem"

Testing

All existing tests continue to pass, and the new functionality is covered by two new test cases.

Closes #22

Original prompt

Can you create the GetProblem method for the solution.Solution interface that matches the signature defined in issue #22?

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.43%. Comparing base (0214315) to head (13ee85f).
⚠️ Report is 10 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #24      +/-   ##
==========================================
+ Coverage   86.76%   87.43%   +0.67%     
==========================================
  Files          27       35       +8     
  Lines        3687     4171     +484     
==========================================
+ Hits         3199     3647     +448     
- Misses        440      470      +30     
- Partials       48       54       +6     

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