Followed PR https://github.com/PaddlePaddle/Paddle/pull/49842 , added Digraph and Shape unit test for `case` and `switch_case`. This PR only contained test changes because `case` and `switch_case` call `cond`. The PR https://github.com/PaddlePaddle/Paddle/pull/49842 has already solved the 0d tensor support.

Add 0d Tensor Test Cases for cond, case, switch_case. Since the 3 APIs are control flow APIs, their support for 0d tensor relies on the underneath APIs. This PR just added test cases to prove that the 3 APIs have already handled 0d tensor well.

* Merge branch 'reduce_sum' of https://github.com/GhostScreaming/Paddle into mine_fluid_clean_common.

* Fix some bugs.

* Clean APIs in python/paddle/fluid/layers/control_flow.py

* Polish code style.

* Change API.

* Fix some bugs.

* Fix some bugs.

* 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

[CodeStyle][NPU] use np.testing.assert_allclose instead of self.assertTrue(np.allclose(...)) (part 1) (#44988)

* autofix

* try resolve precision issues

* revert some changes

* clean some `err_msg`

* 0.0001 -> 1e-4

* update commented assert code

* try to fix some shape errors

* `numpy` -> `np`

* empty commit, trigger kunlun ci, test=kunlun

* empty commit, retrigger kunlun ci, test=kunlun

* empty commit, trigger kunlun ci, try fix npu memcpy_h2d, test=kunlun

* try fix npu import error, test=kunlun

* 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 API switch_case. test=develop

add Nest

* modify code according to reviews:
1.Attr(branch_index) support 'uint8' and 'int64' besides 'int32'.
2.remove useless code.
test=develop

* replace fluid.layers.data with fluid.data and polish API document. test=develop