turtle: TNavigator.degrees(0) raises ZeroDivisionError instead of a clear error

Bug report

turtle.TNavigator.degrees(fullcircle) — the public Turtle.degrees / turtle.degrees — divides
360 / fullcircle in _setDegreesPerAU without checking fullcircle, so passing 0 raises a
ZeroDivisionError that leaks the implementation rather than reporting the invalid argument:

>>> import turtle
>>> turtle.TNavigator().degrees(0)
Traceback (most recent call last):
  ...
ZeroDivisionError: division by zero

degrees documents fullcircle only as "a number", and 0 reaches the division directly through the
public API. It should raise a clear ValueError instead. The companion radians() passes math.tau,
so it is unaffected.

CPython versions tested on:

3.12, 3.14 (main)

Operating systems tested on:

Linux

Linked PRs

• gh-152038

Comienza en turtle.TNavigator.degrees y en la ruta _setDegreesPerAU descrita en el informe; después, ejecuta la reproducción proporcionada turtle.TNavigator().degrees(0). La tarea estará terminada cuando cero sea rechazado a través de la API pública degrees con un ValueError claro en lugar de ZeroDivisionError; comprueba que el comportamiento de radians() siga sin verse afectado.