🧪 Add tests for Dijkstra shortest path solver

[johnstrand]

🎯 What: The testing gap addressed is missing tests for the Dijkstra shortest path solver in src/GameUtils/Entity/Dijkstra.cs.
📊 Coverage: Scenarios now tested include valid paths, favoring lighter paths, disconnected nodes (no path), missing start/end nodes, directed vs undirected edges, start equaling end, initialization from constructor vs add methods, and removing edges.
✨ Result: The improvement in test coverage ensures the behavior of Dijkstra's algorithm solver is robust, deterministic, and well-tested against edge cases.

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PR created automatically by Jules for task 1037102487214172688 started by @johnstrand

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