🧪 [Testing Improvement] Add negative logit tests for Engine.greedyNextToken

[void0x14]

🎯 What: The testing gap addressed
This PR addresses the missing explicit test coverage for Engine.greedyNextToken when resolving sequences where logits fall into exclusively negative values (which are common prior to softmax passes with unnormalized projection weights).

📊 Coverage: What scenarios are now tested

• The greedyNextToken behavior when all probabilities evaluated are functionally negative floats.
• It correctly overrides internal uninitialized 0xaa memory filler during debug bounds testing by setting -100.0 over the slice explicitly, a known Zig standard allocator gotcha.

✨ Result: The improvement in test coverage
The engine inference generation decode path (sampleGreedy) is now verified deterministic across both normal standard operations (positive values) and specific bounds (all negative values).

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PR created automatically by Jules for task 14226148524933231579 started by @ulac000000

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