Support restriction relations with >1 via ways

https://www.openstreetmap.org/relation/8099562

The issue links to an OSM relation (ID 8099562) but provides no context on what needs to be changed in the codebase. Start by examining the linked OSM relation to understand the restriction pattern. Then, look for existing code in osm2streets that handles restriction relations, likely in modules dealing with OSM parsing or street network construction. Determine how the current implementation handles single-via restrictions and what modifications are needed to support multiple via ways. Testing will involve verifying that the converted street network correctly interprets these complex restrictions.

Written by the indexing model from the issue text.