⚡ Verify AStar visited set Contains check complexity

[johnstrand]

💡 What: Added AStarBenchmarks to the benchmark suite and verified that _visited in AStar is already a HashSet, providing O(1) Contains lookups.

🎯 Why: The issue hypothesized an O(N) lookup for _visited.Contains(neighbor), but code analysis confirmed _visited is declared as HashSet _visited = [], which already performs O(1) lookups.

📊 Measured Improvement: Verified that _visited is already a HashSet with O(1) Contains lookups. Added AStarBenchmarks to benchmark pathfinding operations.

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PR created automatically by Jules for task 13873159358295831929 started by @johnstrand

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