⚡ Optimize token normalization loop avoiding list copy

[dioncx]

💡 What: Changed the loop for token in list(expanded): to for token in expanded: in _normalize_tokens() in json_memory/smart.py.
🎯 Why: The list() cast was previously used to avoid a "Set changed size during iteration" RuntimeError. However, the loop only modifies a separate stems set. The expanded set is updated only after the loop completes. Thus, copying the set to a list is unnecessary and creates overhead.
📊 Measured Improvement: Benchmarking 10,000 iterations on a long string showed a decrease in runtime from ~6.4s to ~6.0s.

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PR created automatically by Jules for task 2718501784050577830 started by @dioncx

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