index backed knn pattern

[GregoryCMiller]

loving index support for spatial predicates!

the next most common performance constrained spatial join is probably k nearest neighbors (KNN).

in postgis the canonical KNN pattern is a cross join lateral with an index optimized order by distance (https://postgis.net/workshops/postgis-intro/knn.html).

is there support planned for an index backed knn pattern in duckdb?

[Maxxen]

Yes, Im currently implementing the distance functions natively in spatial instead of relying on GEOS (which already gives like a 2x speedup), but once they're in place in tackling distance joins. I already implemented basically the same thing as part of VSS in this PR