Add custom solution properties to Excel serializer output

[Copilot]

Custom solution properties defined via Solution.customProperties() were only serialized to JSON, not Excel reports.

Changes

Event Model

• Added solutionProperties field to SolutionGeneratedEvent to preserve computed properties through the pipeline
• Updated Executor to pass properties from WorkUnitResult when creating events

Excel Serialization

• Extract unique custom property keys from all results using LinkedHashSet (preserves insertion order)
• Dynamically append custom property columns after standard columns (Instance, Algorithm, Score, etc.)
• Update pivot table area reference to include custom columns
• Use null for missing properties to maintain Excel cell type consistency

Implementation Example

// In your Solution class
@Override
public Map<String, Function<MySolution, Object>> customProperties() {
    return Map.of(
        "vehicleCount", s -> s.countVehicles(),
        "avgDistance", s -> s.calculateAverageDistance()
    );
}

These properties now appear as additional columns in the "Raw Results" sheet, automatically discovered from any solution that defines them.

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