Use region-specific configurable lane widths

Do something like https://github.com/westnordost/osm-legal-default-speeds and write down standard lane widths in different regions, and apply them when there's nothing explicitly tagged in OSM.

Look at the linked repository for region-specific lane width standards. Examine how OSM tags are currently processed in osm2streets to understand where to apply default widths. Determine the configuration format and where to store regional data. Implement fallback logic when explicit OSM tags are missing.

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