* [hotfix] fix zero's incompatibility with checkpoint in torch-1.12
* [zero] add cpu shard init
* [zero] add tiny example test
* [colo_tensor] fix bugs for torch-1.11
* fixes memory leak when paramter is in fp16 in ZeroDDP init.
* bans chunk releasement in CUDA. Only when a chunk is about to offload, it is allowed to release.
* adds a constant placement policy. With it, users can allocate a reserved caching memory space for parameters.
* update gemini mgr
* update chunk
* add docstr
* polish placement policy
* update test chunk
* update test zero
* polish unit test
* remove useless unit test
* add placement policy
* add gemini mgr
* update mem stats collector
* update zero
* update zero optim
* fix bugs
* zero optim monitor os
* polish unit test
* polish unit test
* add assert
