⚡ O(1) CFG successor lookup in IR verifier

[Tcode-Motion]

💡 What: Replaced .iter().find() with a pre-computed HashMap lookup in verify_function of IRVerifier.
🎯 Why: To eliminate O(N) linear searches for each block's successors, significantly improving verifier performance for functions with many basic blocks, reducing overall time complexity from O(V * E) to O(V + E).
📊 Measured Improvement: Reduces CFG verification time complexity, visible via cargo bench -p techscript_optimizer.

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PR created automatically by Jules for task 16169091484459046166 started by @Tcode-Motion

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