[Nezha P0] Add PretrainedConfig and unit tests

[sijunhe]

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PR changes

Description

[paddle-bot]

Thanks for your contribution!

[codecov]

Codecov Report

Merging #4575 (c2a8153) into develop (6a0c50c) will increase coverage by 0.43%.
The diff coverage is 99.18%.

@@             Coverage Diff             @@
##           develop    #4575      +/-   ##
===========================================
+ Coverage    41.31%   41.74%   +0.43%     
===========================================
  Files          433      434       +1     
  Lines        61820    61860      +40     
===========================================
+ Hits         25540    25824     +284     
+ Misses       36280    36036     -244     

Impacted Files	Coverage Δ
paddlenlp/transformers/nezha/modeling.py	93.02% <98.75%> (+72.41%)	⬆️
paddlenlp/transformers/__init__.py	100.00% <100.00%> (ø)
paddlenlp/transformers/bert/modeling.py	90.28% <100.00%> (+0.05%)	⬆️
paddlenlp/transformers/gpt/modeling.py	78.60% <100.00%> (+0.17%)	⬆️
paddlenlp/transformers/nezha/configuration.py	100.00% <100.00%> (ø)
paddlenlp/transformers/nezha/tokenizer.py	88.33% <100.00%> (+47.34%)	⬆️
paddlenlp/utils/downloader.py	58.60% <0.00%> (+0.40%)	⬆️

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[wj-Mcat]

LGTM