Compatibility with Python 3.13

[commongeek]

I use PonyPRM with Python 3.12 on Windows without problem. However after upgrading to 3.13 I got the following error:

File "C:\Users\Administrator\Python313\Lib\site-packages\pony\orm\core.py", line 3578, in select
query = reverse.entity._select_all()
File "C:\Users\Administrator\Python313\Lib\site-packages\pony\orm\core.py", line 4371, in _select_all
return Query(entity.default_iter_name, entity.default_genexpr, {}, { '.0' : entity })
File "C:\Users\Administrator\Python313\Lib\site-packages\pony\orm\core.py", line 5713, in init
pickled_tree = pickle_ast(tree)
File "C:\Users\Administrator\Python313\Lib\site-packages\pony\utils\utils.py", line 383, in pickle_ast
pickler.persistent_id = _persistent_id
^^^^^^^^^^^^^^^^^^^^^
AttributeError: '_pickle.Pickler' object attribute 'persistent_id' is read-only

[black-sliver]

Since 3.13, that method is defined in C, which means we have to subclass the Pickler rather than assigning to the member.

I believe there are other, more complicated problems for py3.13 support tough. I plan to try and implement py3.13 support hopefully later this year if there is no update from the original devs.