* add APIs
* implement save_sharded_model
* add test for hybrid checkpointio
* implement naive loading for sharded model
* implement efficient sharded model loading
* open a new file for hybrid checkpoint_io
* small fix
* fix circular importing
* fix docstring
* arrange arguments and apis
* small fix
* [shardformer/sequence parallel] Support sequence parallel for gpt2 (#4384)
* [sequence parallel] add sequence parallel linear col/row support (#4336)
* add sequence parallel linear col/row support
* add annotation
* add annotation
* add support for gpt2 fused qkv linear layer
* support sequence parallel in GPT2
* add docstring and note
* add requirments
* remove unused flash-attb
* modify flash attn test
* modify flash attn setting
* modify flash attn code
* add assert before divide, rename forward function
* [shardformer/test] fix gpt2 test with seq-parallel
* [shardformer/sequence parallel] Overlap input gather and grad computation during col backward (#4401)
* overlap gather input / grad computing during col backward
* modify test for overlap
* simplify code
* fix code and modify cuda stream synchronize
* [shardformer/sequence parallel] polish code
* add naive optimizer for 3DPlugin/refactor gpt2 shardformer test
* merge tests of PP/DP/TP combinations into one test file
* fix bug when sync grad for dp in HybridPlugin
* update supported precisions for 3DPlugin/fix bug when shifting tp_degree
* improve the passing of lazy_init
* modify lazy_init/use sync_shared_params