Some optimization suggestions for reducing CPU usage

[ali-pahlevani]

💢 Optimizations:

File	Optimization	Description	Estimated CPU Usage Reduction
Registration.cpp	Vectorized TransformPoints	Use Eigen matrix operations instead of per-point std::transform	5–15% of total runtime
Registration.cpp	Precomputed kernel_squared	Compute kernel * kernel once instead of repeatedly in Weight	0.5–1% of total runtime
Registration.cpp	Improved Weight Function	Reduce operations in weight computation from 4 to 2 multiplications + 1 addition	2–5% of total runtime
VoxelHashMap.cpp	Squared Distance in GetClosestNeighbor	Use .squaredNorm() for comparisons, with one sqrt at the end	10–20% of total runtime
VoxelHashMap.cpp	Precomputed Statistics in GetClosestNeighbor	Use sum_points and sum_outer for O(27) computation vs. O(27 * P) per query	15–25% of total runtime
VoxelHashMap.cpp	Efficient AddPoints	Simplify with for loop and map_.at(), maintaining precomputed stats	1–3% of total runtime
VoxelHashMap.cpp	Optimized RemovePointsFarFromLocation	Use iterator-based erase for safe and efficient removal	1–2% of total runtime
Overall	Combined Effect	Cumulative impact across all optimizations, varying with point cloud size and voxel density	20–50% of total runtime

[Daehan2Lee]

Thanks for the optimization! I'll profile the changes this week and let you know which parts we can merge.

[ali-pahlevani]

Thanks for the optimization! I'll profile the changes this week and let you know which parts we can merge.

Thank you for letting me ask for a pull request.
Great. I'll be eagerly waiting for your review.