Did you ever find a solution to this? Suffering a similar issue...

Is there anything documented about how to do this specifically?

Update, communicated with the people at the geoswift library to implement the "prepared geometry" function of geos into the library. Implementation: Map the geometry of each of your features to a PreparedGeometry by calling the new makePrepared() method, and store those values somewhere alongside the original features/properties. At each location update use one of the new contains methods on PreparedGeometry to test for containment. https://github.com/GEOSwift/GEOSwift/pull/264