[checkpointio] Unsharded Optimizer Checkpoint for Gemini Plugin

[Fridge003]

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design: #4140

📝 What does this PR do?

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• Implement the unsharded optimizer checkpointing feature through overloading state_dict()/load_state_dict() methods for ZeroOptimizer.
• Support compatibility with pytorch model/optimizer checkpoints and add relevant tests.

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[github-actions]

The code coverage for the changed files is 89%.

Click me to view the complete report

Name                                                    Stmts   Miss  Cover
---------------------------------------------------------------------------
colossalai/booster/plugin/gemini_plugin.py                117     14    88%
colossalai/checkpoint_io/checkpoint_io_base.py             66      9    86%
colossalai/checkpoint_io/general_checkpoint_io.py         107      8    93%
colossalai/checkpoint_io/utils.py                         250     44    82%
colossalai/interface/optimizer.py                          42      6    86%
colossalai/nn/optimizer/cpu_adam.py                        70      4    94%
colossalai/nn/optimizer/fused_adam.py                      57     11    81%
colossalai/nn/optimizer/hybrid_adam.py                     65      3    95%
colossalai/testing/comparison.py                           40      6    85%
colossalai/zero/gemini/gemini_optimizer.py                378     34    91%
tests/test_checkpoint_io/test_gemini_checkpoint_io.py      72      0   100%
---------------------------------------------------------------------------
TOTAL                                                    1264    139    89%

[github-actions]

The code coverage for the changed files is 89%.

Click me to view the complete report

Name                                                        Stmts   Miss  Cover
-------------------------------------------------------------------------------
colossalai/booster/plugin/gemini_plugin.py                    114     12    89%
colossalai/checkpoint_io/checkpoint_io_base.py                 66      9    86%
colossalai/checkpoint_io/general_checkpoint_io.py             107      8    93%
colossalai/checkpoint_io/utils.py                             250     44    82%
colossalai/interface/optimizer.py                              42      5    88%
colossalai/nn/optimizer/cpu_adam.py                            70      4    94%
colossalai/nn/optimizer/fused_adam.py                          57     11    81%
colossalai/nn/optimizer/hybrid_adam.py                         65      3    95%
colossalai/testing/comparison.py                               77     21    73%
colossalai/zero/gemini/gemini_optimizer.py                    358     34    91%
tests/test_checkpoint_io/test_gemini_checkpoint_io.py          84      0   100%
tests/test_checkpoint_io/test_gemini_torch_compability.py     116      0   100%
-------------------------------------------------------------------------------
TOTAL                                                        1406    151    89%

[Fridge003]

[Fridge003]