sign of complex 0+0j returns complex nan #166
Description
Example:
In [3]: import array_api_strict as aa
In [4]: z = aa.zeros(1, dtype=aa.complex128)
In [5]: aa.sign(z)
/home/warren/py3.13.5/lib/python3.13/site-packages/array_api_strict/_array_object.py:970: RuntimeWarning: invalid value encountered in divide
res = self._array.__truediv__(other._array)
Out[5]: Array([nan+nanj], dtype=array_api_strict.complex128)
The result should be Array([0+0j], ...).
Special handling of the complex case was added in #74, but that change didn't consider the input 0+0j.