fix: clamp s_offset overshoot at road boundaries

These changes aim to clamp s-offset overshoots whenever these occur.

A notable case is that of a route waypoint which points to, for example, s=20m on a road with length 20m. As the route waypoint is shifted by an entity's bounding box center, a conversion from s=20 + entity_length/2 to world coordinates would be attempted. With these changes, an s_offset which exceeds the bounds of a road will be clamped and a warning will be emitted.