pybricks.robotics.Car: Raise error on no car built.

We get quite a few questions about the Xbox controller not connecting,
when the actual issue is the car initialization never completing because
no car has been built yet. To be more explicit, raise an error if the endpoint
is not found within 10 seconds.

Fixes pybricks/support#1564

CHANGELOG.md

@@ -14,10 +14,13 @@
 
 ### Changed
 - Allow single floating point value for brightness array ([support#1547]).
+- Raise a descriptive error when the `Car` class can't find a steering mechanism
+  end stop within 10 seconds ([support#1564]).
 
 [support#1024]: https://github.com/pybricks/support/issues/1024
 [support#1537]: https://github.com/orgs/pybricks/discussions/1537
 [support#1547]: https://github.com/pybricks/support/issues/1547
+[support#1564]: https://github.com/pybricks/support/issues/1564
 
 ## [3.4.0] - 2024-03-11
 

pybricks/robotics/pb_type_car.c

@@ -50,11 +50,16 @@ STATIC int32_t run_until_stalled_blocking(pbio_servo_t *srv, pbio_direction_t di
     int32_t speed = (direction == PBIO_DIRECTION_CLOCKWISE ? 1 : -1) * 300;
     pb_assert(pbio_servo_run_until_stalled(srv, speed, torque_limit, PBIO_CONTROL_ON_COMPLETION_COAST));
 
+    uint32_t start_time = mp_hal_ticks_ms();
+
     // Wait for the movement to complete or be cancelled.
     while (!pbio_control_is_done(&srv->control)) {
         if (!pbio_servo_update_loop_is_running(srv)) {
             pb_assert(PBIO_ERROR_NO_DEV);
         }
+        if (mp_hal_ticks_ms() - start_time > 10000) {
+            mp_raise_msg(&mp_type_RuntimeError, MP_ERROR_TEXT("The steering mechanism has no end stop. Did you build a car yet?"));
+        }
         mp_hal_delay_ms(10);
     }