⚡ Bolt: Avoid costly sqrt and use early exits in hot distance scans

[teerthsharma]

💡 What: Replaced exact distance computation (libm::sqrt) with a squared distance comparison and early loop exit in ManifoldPoint::is_neighbor.
🎯 Why: SparseAttentionGraph::add_point uses is_neighbor in a hot O(N) spatial scan. Calculating full distances wastes cycles processing dimensions past the threshold and computing sqrt when points are already evidently beyond the epsilon radius.
📊 Impact: Speeds up spatial distance checks in high-dimensional or dense manifolds by avoiding floating-point sqrt operations and breaking out of calculation loops early.
🔬 Measurement: Verify correctness by running cargo test -p aether-core manifold, which tests points crossing thresholds.

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PR created automatically by Jules for task 9981737551305813232 started by @teerthsharma

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