Use the original computer drivers, car collisions and towing

Decoded from SKIDMARKS_CD32:

- Computer drivers: the path of nodes laid 2 game units apart along
  the middle of the road, with side points 1 unit in from each wall.
  Drivers aim four nodes past where they'll be in four frames, or cut
  to the other side two nodes on at 70% throttle when running wide.
  Replaces the pure-pursuit AI; laps are quicker on every track.
- Collisions: six points on the player's car (corners and sides, from
  .set words 6 and 7, now known to be half-length and half-width) are
  tested against the other car's box. Hits push the cars apart with a
  strength that grows with their speed difference, and spin the car.
  As in the original, only human players' cars collide; cars at
  different heights don't.
- Towing: the hitch is at the car's back, the caravan sits 0.656 units
  behind it, and past 90 degrees both car and caravan bend back.

The reconstructed collision weight (`mass`) is gone; old asset files
with it still load.

src/main.rs

@@ -411,7 +411,7 @@ fn render_shot(data: GameData, args: &Args) -> Result<(), String> {
             .entrants
             .iter_mut()
             .filter(|e| matches!(e.driver, game::Driver::Human(_)))
-            .map(|e| e.ai.drive(&e.car, &race.track, game::DT, true))
+            .map(|e| e.ai.drive(&e.car, &race.path, game::DT, true))
             .collect();
         race.step(&controls);
         app::draw_race(&mut frame, &app.data, &race, &mut cams, players);