* 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
* polish chunk manager
* polish unit test
* impl add_extern_static_tensor for chunk mgr
* add mem stats collector v2
* polish code
* polish unit test
* polish code
* polish get chunks