[Python] My ArrivalTimeUpdatingVariableListener is not working, how to make it work

I am developing route optimiser using timefold python but ArrivalTimeUpdatingVariableListener is not running I also included print statement to check if it's running in background or not. I have used the code that was given in the tests folder in timefold_solver_python official repo. link: https://github.com/TimefoldAI/timefold-solver-python/blob/main/tests/test_vehicle_routing.py#L28

My code:

`class ArrivalTimeUpdatingVariableListener(VariableListener):
@staticmethod
def calculate_arrival_time(customer: Optional['Customer'], previous_departure_time: Optional[datetime]) \
-> datetime | None:
if customer is None or previous_departure_time is None:
return None
return previous_departure_time + timedelta(seconds=customer.drivingTimeSecondsFromPreviousStandstill)

def after_variable_changed(self, score_director: ScoreDirector, customer: 'Customer') -> None:
print("b")
if customer.vehicle is None:
if customer.arrival_time is not None:
score_director.before_variable_changed(customer, 'arrival_time')
customer.arrival_time = None
score_director.after_variable_changed(customer, 'arrival_time')
return None
previous_customer = customer.previous_customer
departure_time = customer.vehicle.departure_time if previous_customer is None \
else previous_customer.get_departure_time()
next_customer = customer
arrival_time = ArrivalTimeUpdatingVariableListener.calculate_arrival_time(next_customer, departure_time)
while next_customer is not None and next_customer.arrival_time != arrival_time:
score_director.before_variable_changed(next_customer, 'arrival_time')
next_customer.arrival_time = arrival_time
score_director.after_variable_changed(next_customer, 'arrival_time')
departure_time = next_customer.get_departure_time()
next_customer = next_customer.next_customer
arrival_time = ArrivalTimeUpdatingVariableListener.calculate_arrival_time(next_customer, departure_time)


@planning_entity
class Customer(JsonDomainBase):
id: Annotated[str, PlanningId]
name: Optional[str] = None
location: Annotated[Location, LocationSerializer, LocationValidator]
ready_time: datetime
due_time: datetime
service_duration: timedelta
demand: int
vehicle: Annotated[Optional['Vehicle'], InverseRelationShadowVariable(
source_variable_name='customers'), IdSerializer, VehicleValidator, Field(default=None)]
previous_customer: Annotated[Optional['Customer'], PreviousElementShadowVariable(
source_variable_name='customers'), IdSerializer, CustomerValidator, Field(default=None)]
next_customer: Annotated[Optional['Customer'], NextElementShadowVariable(
source_variable_name='customers'), IdSerializer, CustomerValidator, Field(default=None)]
arrival_time: Annotated[Optional[datetime], ShadowVariable(
variable_listener_class=ArrivalTimeUpdatingVariableListener,
source_variable_name='vehicle'), ShadowVariable(
variable_listener_class=ArrivalTimeUpdatingVariableListener,
source_variable_name='previous_customer'), Field(default=None)]



I have tried to debug but nothing was printing, I want arrival time

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