Feature

Many existing test cases check that pickle.dumps and pickle.loads of a given type return the exact same value. Almost failed pickle test in RustPython, lack __reduce__ method.

• arrayiterator.__reduce__ (test_array::test_iterator_pickle)
• filter.__reduce__ (test_builtin::test_filter_pickle)
• map.__reduce__ (test_builtin::test_map_pickle)
• ImportError.__reduce__ (test_exceptions::test_copy_pickle)
• OSError.__reduce__
• BaseException.__reduce__ — #3665
• method.__reduce__
• groupby.__reduce__
• _grouper.__reduce__
• tee.__reduce__
• cycle.__reduce__
• dropwhile.__reduce__
• takewhile.__reduce__
• islice.__reduce__
• starmap.__reduce__
• chain.__reduce__
• product.__reduce__
• combinations.__reduce__
• combinations_with_replacement.__reduce__
• permutations.__reduce__
• accumulate.__reduce__
• compress.__reduce__
• filterfalse.__reduce__
• count.__reduce__
• zip_longest.__reduce__
• NotImplemented.__reduce__
• types.SimpleNamespace.__reduce__

These listed elements are almost similar and quite simple to implement.
Please take a look at many PR and existing codes for __reduce__