🧪 Add test for greedyNextToken with negative logits

[void0x14]

🎯 What: The testing gap in Engine.greedyNextToken was addressed by adding an edge case test where all valid logits are negative.
📊 Coverage: The scenario where logits are negative is now fully tested, preventing the uninitialized 0xaa (-3.03e-13 in f32) values from incorrectly passing as the maximum.
✨ Result: Test coverage for greedyNextToken is improved, and logic fragility around negative logits is solved.

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PR created automatically by Jules for task 4016723168567843465 started by @ulac000000

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