🧪 [Testing Improvement] Enhance ArrayList pop test coverage

[void0x14]

🎯 What: The ArrayList.pop functionality has been tested for popping multiple times from an empty list.
📊 Coverage: Popping multiple times on an empty list is now tested, which ensures length does not underflow and the method correctly returns null.
✨ Result: Test coverage for ArrayList edge cases is improved.

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PR created automatically by Jules for task 4553166744959373645 started by @ulac000000

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