🧪 [Testing Improvement] Add ArrayList Pop Functionality Tests

[void0x14]

🎯 What: Added missing test coverage for ArrayList.pop functionality to ensure its behavior is correctly validated, especially on edge cases like empty lists.
📊 Coverage: The new test suite covers:

• Popping from a freshly initialized (empty) list.
• Popping from a list after calling .clear().
• Popping elements that were just appended, ensuring correctness.
  ✨ Result: Test coverage for ArrayList.pop is now explicit and complete, providing extra safety for future refactoring and ensuring empty-list edge cases correctly return null as designed.

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PR created automatically by Jules for task 384207186616905542 started by @ulac000000

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