⚡ Bolt: Optimize spatial scan via inline squared distance in ManifoldPoint::is_neighbor

[teerthsharma]

💡 What: Optimized ManifoldPoint::is_neighbor by replacing the standard Euclidean distance check (which uses an expensive sqrt operation) with an inline squared distance calculation and an early exit condition.

🎯 Why: In SparseAttentionGraph::add_point, the is_neighbor function is a hot path called frequently during point addition (O(N) spatial scan). Avoiding sqrt and exiting early drastically reduces processing overhead in this critical section.

📊 Impact: Significantly reduces the computational overhead of constructing the sparse attention graph by eliminating libm::sqrt calls and bypassing full distance calculations when thresholds are exceeded early.

🔬 Measurement: Run the test suite (cargo test -p aether-core) to verify that the topological clustering and manifold embedding tests pass perfectly. The exact distance is no longer computed when unnecessary, improving throughput.

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PR created automatically by Jules for task 4643858045170319191 started by @teerthsharma

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