Change incompatible pointer type from RadixNodeObject to PyObject

[robert-scheck]

Since GCC 14 implicitly casting all pointer types to all other pointer types is no longer allowed. This behavior is now restricted to the void * type and its qualified variations. According to the Python 3 documentation, all object types are extensions of the PyObject type. And it looks like the RadixNodeObject should meet the conditions to be a proper Python object.

See also:

• https://gcc.gnu.org/gcc-14/porting_to.html#warnings-as-errors
• https://docs.python.org/3/c-api/list.html#c.PyList_Append
• https://docs.python.org/3/c-api/structures.html#c.PyObject

Fixes: #57

Thanks to @musicinmybrain and @mbattista for their input and suggestions.

[glaubitz]

I can confirm that this patch fixes the problem for me.