fix: resolve thread safety issues in simulation engine

[YJack0000]

Summary

• Make static RNG thread_local in Organism::makeMove() and Genes::defaultMutationLogic() to fix data races
• Pre-compute organism list once before thread dispatch instead of calling getAllOrganisms() per-thread (was doing N expensive dynamic_pointer_cast scans)
• Skip std::thread creation overhead when numThreads=1
• Make handleInteractions single-threaded since it mutates shared state (food->eaten(), organism->killed(), lifeSpan modifications)
• Keep handleReactions multi-threaded (safe: each thread only writes to its own organism's movement/reactionCounter)
• Use std::atomic<FoodState> for thread-safe food state transitions
• Use safe objectsMapper.find() instead of operator[] in threaded context
• Fix shared_ptr passed by value in calculateDistance (now const ref)
• Make react()/interact() take const vector references
• Remove dead removeDeadOrganisms() declaration
• Remove commented-out debug printf statements

Discussion Points

• handleInteractions 目前改為 single-threaded 來避免 data race。如果未來需要平行化 interaction phase，可以考慮用 per-object lock 或將 interaction 結果收集後 batch apply
• Food::canBeEaten() 用 std::atomic<FoodState> 但兩個 organism 仍可能同時看到 FRESH 然後都加 energy。目前這是 acceptable 因為 interaction phase 已改為 single-threaded

Test plan

• All 3 existing Python tests pass
• Run benchmark example to verify no performance regression
• Test with numThreads > 1 to verify reaction phase parallelism still works

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