* initial commit, add code for async construct tensor from numpy array

* inital commit to change Maybe to Optional

* delete redundant code

* replace Maybe with Optional

* fix compile errors

* format code

* changes based on review

* format code, fix based on review

* format code

* fix multiclient type

* changes based on review

* changes based on review

* unify calling to IsMultiClirnt

* refector multi_client related code

* restore InMultiClient interface

* double check for unnecessary changes

* remove unnecessary changes

* format code

* Update oneflow/api/python/symbol/job_conf_symbol.cpp

* Update oneflow/api/python/symbol/op_conf_symbol.cpp

* Update oneflow/api/python/symbol/op_node_signature_symbol.cpp

* Update oneflow/core/common/optional.h

* Update oneflow/api/python/symbol/string_symbol.cpp

* Update oneflow/api/python/symbol/scope_symbol.cpp

* Update oneflow/api/python/symbol/placement_symbol.cpp

* Update oneflow/api/python/symbol/op_conf_symbol.cpp
Co-authored-by: NHoujiang Chen <chenhoujiangcug@gmail.com>
Co-authored-by: NTwice <i@twice.moe>