Support __copy__ and __deepcopy__?

`juliacall.AnyValue.__copy__` and `__deepcopy__` could call Julia's `copy` and `deepcopy`.

Conversely, `copy(::Py)` and `deepcopy_internal(::Py, ::IdDict)` could call Python's `copy.copy` and `copy.deepcopy`.

https://docs.python.org/3/library/copy.html

Start with the Julia APIs named in the issue: juliacall.AnyValue.__copy__, __deepcopy__, copy(::Py), and deepcopy_internal(::Py, ::IdDict). Read the linked Python copy documentation and trace the existing Julia/Python object-copy entry points. Done means the requested copy and deepcopy operations delegate correctly in both directions, with behavior verified by appropriate tests.

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