Add comprehensive tests for SimplexSolution and TableauAlgorithmState

[Copilot]

This PR adds comprehensive test coverage for the SimplexSolution and TableauAlgorithmState objects to improve code quality and maintainability.

SimplexSolution Tests

Created a new test file testing/solution/simplex_solution_test.go with 9 comprehensive tests covering all public methods:

• GetValueMap() - Verifies correct retrieval of variable values mapping
• GetOptimalValue() - Validates objective value retrieval
• GetStatus() - Tests multiple solution statuses (OPTIMAL, INFEASIBLE, UNBOUNDED)
• GetProblem() - Validates problem retrieval with and without attached optimization problems
• Edge cases - Tests empty variable values and complete structure validation

Result: 100% coverage of SimplexSolution's public interface

TableauAlgorithmState Tests

Enhanced testing/algorithms/tableau/state_test.go with 13 new tests significantly increasing coverage:

State Validation

• Check() - Tests valid states and error handling for invalid states (e.g., negative iteration count)
• CheckTerminationCondition() - Validates termination detection for both in-progress and optimal states

Variable Management

• GetBasicVariables() / GetNonBasicVariables() - Verifies correct variable partitioning
• NumberOfIterations() / NumberOfVariables() / NumberOfConstraints() - Validates state metrics

Computational Methods

• GetReducedCostVector() - Tests reduced cost vector computation
• GetShadowPrice() - Validates shadow price calculations
• CreateOptimalValuesMap() - Tests optimal value mapping with known expected results
• ToSolution() - Validates conversion to SimplexSolution with proper status and values

Testing Approach

All tests follow existing repository conventions and patterns:

• Use established test infrastructure (e.g., examples.GetTestProblem5())
• Validate against known solutions from well-documented examples
• Include both positive and negative test cases
• Provide clear documentation for each test's purpose

Verification

✅ All 22 new tests pass successfully
✅ All existing tests continue to pass
✅ Code builds without errors
✅ Code review feedback addressed

These tests will help catch regressions early and ensure the reliability of core simplex solver components.

Original prompt

Can you add tests for the SimplexSolution object in the targeted branch? Can you also propose some tests for the TableauAlgorithmState object to increase code coverage?

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 48.80%. Comparing base (1882ae9) to head (da52fb7).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main       #3      +/-   ##
==========================================
+ Coverage   41.18%   48.80%   +7.61%     
==========================================
  Files          16       16              
  Lines        1549     1549              
==========================================
+ Hits          638      756     +118     
+ Misses        859      728     -131     
- Partials       52       65      +13     

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