TreeKernelSum: Fast Approximate All-Pairs Kernel Summation on Weighted Trees

Rust implementation of a near-linear-time algorithm for all-pairs kernel summation on weighted trees. Given a tree T on n nodes with edge weights, node values mu, and a smooth kernel K, computes Phi(v) = sum_u K(d_T(v,u)) mu(u) for all v in O(r n log n) time via centroid decomposition and sum-of-exponentials approximation. Includes: correctness validation (single-exponential exactness, general kernel error bounds), performance benchmarks up to 1M nodes (972x speedup at n=50k), sinc-quadrature SOE fitting (r=8 at epsilon=1e-8), phylogenetic OU kernel summation on real mammal phylogenies (Fritz 5020sp, Upham 5912sp), and Nadaraya-Watson kernel prediction of mammalian body mass (R^2=0.955). Accompanying manuscript included in paper/paper.tex.