Improve snapping radius implementation

In the current implementation of snapping radius the limit is applied on top of the result returned by the `findClosest` method of `LocationIndex` class. Instead, investigate options to pass the radius directly to the lookup query in order to avoid searching an unnecessarily large area, and to be able to expand the search radius on a per-query basis (basically, override the `location_index_search_iterations` config file setting).

A potential starting point to look into could be the `LocationIndexTree.findNClosest` method.