⚡ Bolt: avoid libm::sqrt in Sparse Attention Graph spatial scans

[teerthsharma]

💡 What: Replaced the full distance() < epsilon calculation in ManifoldPoint::is_neighbor with an inline loop that computes squared distances and exits early if the accumulated sum exceeds epsilon^2.
🎯 Why: The is_neighbor function is a critical bottleneck called inside the inner O(N) loop of SparseAttentionGraph::add_point. Computing the libm::sqrt and evaluating all dimensions for distant points introduces severe computational overhead.
📊 Impact: Significantly accelerates point additions in the topological pipeline by avoiding sqrt and short-circuiting distance evaluations.
🔬 Measurement: Verify by running cargo test -p aether-core and observing no regressions in manifold::tests::test_sparse_attention_neighbor and test_point_distance. Run micro-benchmarks on add_point to measure latency improvements.

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PR created automatically by Jules for task 4446327687940072145 started by @teerthsharma

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