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