[Unified checkpoint] PR cherry-picks (#9277)

* [Unified Checkpoint] Support expert parallel (#9055)

* update code

* [Unified Checkpoint] Fix generation config save (#9223)

* [Unified Checkpoint] update async_save_info in develop (#9173)

* [Unified Checkpoint] update async save logic (#9274)

* update async save signal

* fix async save hang

* bug fix

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Co-authored-by: Weiguo Zhu <DrownFish19@gmail.com>