replace cross_entropy in python/paddle/fluid/tests/unittests/test_[a-n]*.py except test_dist_transpiler.py (#48913)

* update config

* re-blacken python code

* temporarily disable date and diff_py_file

* skip a format

* [CodeStyle] remove all future import

* revert test_error.py

* restore future import in example code

* use yapf to format all python file

* yapf exclude two unittests file for they rely on writing and reading file, and format will break them

* disable diff_py_file because too many diff files cause command following failed

* add persistent_workers. test=develop

* fix dataloader. test=develop

* DataLoader support not auto collate batch. test=develop

* add IterableDataset support in multiprocess DataLoader. test=develop

* add pin memory control

* fix buffered reader init problem

* fix unittest error

* add unittest for coverage

* simplify buffered reader to improve DataLoader performance

* fix 22 failed unittests

* fix cuda pinned context condition

* fix test_reader_reset failed

* fix two failed unittests

* change unittest place

* polish error messaage

* polish cast op GetExpecctedKernelType

* remove debug info in unittest

* fix test_multiprocess_dataloader_static random fail. test=develop

* add DataLoader, Dataset, BatchSampler