[Gradient Compression] Refactor CommHookInterface and PythonCommHook.

[wayi1]

Stack from ghstack:

• [Gradient Compression] Add CppCommHook subclass for supporting the C++ API of communication hook. #46566 [Gradient Compression] Add CppCommHook subclass for supporting the C++ API of communication hook.
• [Gradient Compression] Refactor CommHookInterface and PythonCommHook. #46512 [Gradient Compression] Refactor CommHookInterface and PythonCommHook.

1. Merge 1-line PythonCommHook constructor into the header for simplicity.
2. Move the implementation of PythonCommHook destructor from the header file to cpp file.
3. Rename processFuture method as parseHookResult for readability.
4. Simplify some comments.

Original PR issue: C++ DDP Communication Hook #46348

Differential Revision: D24374282

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This comment has been revised 4 times.

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💊 CI failures summary and remediations

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This comment has been revised 64 times.

[pritamdamania87]

Code changes look good, although it seems like the windows tests are failing with an error like:

comm.cpp.obj : error LNK2019: unresolved external symbol "__declspec(dllimport) public: virtual __cdecl c10d::CommHookInterface::~CommHookInterface(void)" (__imp_??1CommHookInterface@c10d@@UEAA@XZ) referenced in function "public: virtual __cdecl c10d::PythonCommHook::~PythonCommHook(void)" (??1PythonCommHook@c10d@@UEAA@XZ)
init.cpp.obj : error LNK2019: unresolved external symbol "__declspec(dllimport) public: __cdecl c10d::CommHookInterface::CommHookInterface(void)" (__imp_??0CommHookInterface@c10d@@QEAA@XZ) referenced in function "class std::unique_ptr<class c10d::PythonCommHook,struct std::default_delete<class c10d::PythonCommHook> > __cdecl std::make_unique<class c10d::PythonCommHook,class pybind11::object,class pybind11::object,0>(class pybind11::object &&,class pybind11::object &&)" (??$make_unique@VPythonCommHook@c10d@@Vobject@pybind11@@V34@$0A@@std@@YA?AV?$unique_ptr@VPythonCommHook@c10d@@U?$default_delete@VPythonCommHook@c10d@@@std@@@0@$$QEAVobject@pybind11@@0@Z)
bin\torch_python.dll : fatal error LNK1120: 2 unresolved externals

[codecov]

Codecov Report

Merging #46512 into gh/SciPioneer/15/base will increase coverage by 0.00%.
The diff coverage is n/a.

@@                  Coverage Diff                   @@
##           gh/SciPioneer/15/base   #46512   +/-   ##
======================================================
  Coverage                  68.96%   68.96%           
======================================================
  Files                        434      434           
  Lines                      55996    55996           
======================================================
+ Hits                       38619    38620    +1     
+ Misses                     17377    17376    -1     

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This pull request has been merged in a6cd294.