* sharded optimizer checkpoint for gemini plugin
* modify test to reduce testing time
* update doc
* fix bug when keep_gatherd is true under GeminiPlugin
* [bf16] add bf16 support for fused adam (#3844)
* [bf16] fused adam kernel support bf16
* [test] update fused adam kernel test
* [test] update fused adam test
* [bf16] cpu adam and hybrid adam optimizers support bf16 (#3860)
* [bf16] implement mixed precision mixin and add bf16 support for low level zero (#3869)
* [bf16] add mixed precision mixin
* [bf16] low level zero optim support bf16
* [text] update low level zero test
* [text] fix low level zero grad acc test
* [bf16] add bf16 support for gemini (#3872)
* [bf16] gemini support bf16
* [test] update gemini bf16 test
* [doc] update gemini docstring
* [bf16] add bf16 support for plugins (#3877)
* [bf16] add bf16 support for legacy zero (#3879)
* [zero] init context support bf16
* [zero] legacy zero support bf16
* [test] add zero bf16 test
* [doc] add bf16 related docstring for legacy zero