[WIP][Unified Checkpoint] Add split param and refactor code

[DesmonDay]

PR types

New features

PR changes

Others

Description

1. Support sharding stage1 v2 for unified checkpoint.
2. Refactor uc code.

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[codecov]

Codecov Report

Attention: Patch coverage is 11.15312% with 940 lines in your changes missing coverage. Please review.

Project coverage is 53.03%. Comparing base (697a4cc) to head (ae9ddce).
Report is 1 commits behind head on develop.

Files with missing lines	Patch %	Lines
...dlenlp/trainer/plugins/unified_checkpoint_utils.py	12.25%	351 Missing ⚠️
...enlp/trainer/plugins/unified_checkpoint_dynamic.py	9.12%	259 Missing ⚠️
.../trainer/plugins/unified_checkpoint_sharding_v2.py	7.52%	172 Missing ⚠️
.../trainer/plugins/unified_checkpoint_single_card.py	13.79%	125 Missing ⚠️
paddlenlp/trainer/plugins/unified_checkpoint.py	23.52%	26 Missing ⚠️
paddlenlp/utils/nested.py	14.28%	6 Missing ⚠️
paddlenlp/trainer/trainer.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #9240      +/-   ##
===========================================
- Coverage    53.09%   53.03%   -0.07%     
===========================================
  Files          657      661       +4     
  Lines       106521   106771     +250     
===========================================
+ Hits         56557    56622      +65     
- Misses       49964    50149     +185     

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[DrownFish19]

这个函数是不是和load_unified_optimizer_locally大部分逻辑相似

[DesmonDay]

目前初步开发中，后续会修改