feat: region-based road width factor with shoulder widths

[Copilot]

Road widths were uniform across regions despite real-world variation — US/Canadian roads are notably wider than European equivalents. This adds a mathematical width model that accounts for lanes, road-type shoulder widths, and a per-region multiplier.

Width formula

lanes > 0:  width = (lanes × 3.5m + shoulderWidth(roadType)) × regionFactor(region)
lanes == 0: width = baseTableWidth(roadType) × regionFactor(region)

New: RegionWidthFactors class

• GetWidthFactor(RegionType) — region multipliers: NA=1.10, EU/Boreal/Mediterranean=1.00, Desert=0.95, Arctic/Tropical=0.90, Steppe=0.85
• GetShoulderWidth(RoadType) — total shoulder (both sides): Motorway=6m, Trunk=5m, Primary=3m, Secondary=1.5m, Tertiary=1m, Residential=0.5m, Service/Dirt/Path/Cycleway=0m

New RegionType.TemperateNorthAmerica

US and Canada are split out from Temperate (Europe/East Asia) into a dedicated TemperateNorthAmerica enum value. OSMParser maps US/CA country codes to this new type. RegionTextures uses the same asphalt/wall/roof textures as Temperate with concrete kerb (matching NA infrastructure style).

RoadMeshExtruder changes

• New overload: GetWidthForRoadType(RoadType, int lanes, RegionType region) — applies full formula above
• ExtrudeWithDetails(RoadType, ...) now uses the region-aware overload instead of the lane-only one, so region is factored into mesh width automatically
• Existing 1-arg and 2-arg overloads are unchanged for backward compatibility

Original prompt

the width of roads doesn't quite match real life yet.

one factor is regionality - US roads are typically wider than most other countries.

Create a region based width factor with reasonable defaults for specific countries. come up with a mathematic function for road width - then the overall width of the roads is a function of the # of lanes for the road, width of the shoulders based on road type, and region width constant.

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