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) — add arrayiter.__reduce__ #3868
• filter.__reduce__ (test_builtin::test_filter_pickle) — add filter.__reduce__ #3732
• map.__reduce__ (test_builtin::test_map_pickle) — Add map.reduce() #3734
• ImportError.__reduce__ (test_exceptions::test_copy_pickle) — Implemented __reduce__ method for the ImportError exception #4973
• OSError.__reduce__ — Add OSError.__reduce__ #4191
• BaseException.__reduce__ — Add BaseException.__reduce__ #3665
• method.__reduce__ — Add method.__reduce__ #4237
• groupby.__reduce__
• _grouper.__reduce__
• tee.__reduce__
• cycle.__reduce__
• dropwhile.__reduce__ — Add dropwhile.__reduce__ #4201
• takewhile.__reduce__ — add takewhile.__reduce__ #4190
• islice.__reduce__ — Implement islice.__reduce__ #4390
• starmap.__reduce__ — Add itertools.starmap.__reduce__ #3988
• chain.__reduce__ — Chain reduce #4232
• product.__reduce__ [VM] Object pickling implementation for product object (python itertools)  #5089
• combinations.__reduce__ — Add itertool.combinations.__reduce__ method #3931, Add combinations.__reduce__  #4272
• combinations_with_replacement.__reduce__
• permutations.__reduce__ added __reduce__ method for itertools.permutations #5029
• accumulate.__reduce__ Implement itertools.accumulate.__reduce__ and __setstate__ #4434
• compress.__reduce__ — Add itertools.compress.__reduce__ #3791
• filterfalse.__reduce__ — Add filterfalse.__reduce__ #3745
• count.__reduce__ — Add count.reduce() #3737
• zip_longest.__reduce__ Add reduce and setstate for zip_longest #4235
• NotImplemented.__reduce__ — Add NotImplemented.__reduce__() #3738
• types.SimpleNamespace.__reduce__ Implemented __reduce__ method for types.SimpleNamespace #4975

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