⚡ Bolt: Optimize dominator tree HashSet allocations

[Tcode-Motion]

💡 What: Replaced repeated HashSet allocations and cloning inside the iterative dominator tree solver loop with a single pre-allocated HashSet that uses .clear(), .extend(), and .retain() for in-place intersections. We also use .clone_from() for updating existing dominator sets.
🎯 Why: Prevents excessive HashSet allocations inside a tight inner loop, which significantly hurt performance during dataflow analysis.
📊 Impact: Reduces heap allocations and speeds up the dominator analysis compiler pass by avoiding O(N) intermediate HashSet instantiations per block per loop iteration.
🔬 Measurement: Run the test suite and benchmark suite to verify the logic remains correct while reducing peak memory usage and compilation time.

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PR created automatically by Jules for task 6626739967144321662 started by @Tcode-Motion

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