Build the web cone query's topology while the map loads

The Dart query found wall crossings and vertex topology on its first
cone, a 25 to 45 ms stall the first time a cone was dragged on each map.
Build them when the map's sightlines load instead, only when the native
library is unavailable.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
a11220fe04Dara Adedeji committed on 10/5/2026, 10:58:23 PMparent11da90d

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