[Draft] Introduce NVSHMEM based communication API for pytorch

[gdengk]

Description

This PR uses pybinding to create NVSHMEM based APIs for pytorch.
Currently we have P2P and a draft implementation of CE based AG.

Still saw some device linking warnings to be cleaned up.

Need to provide NVSHMEM_HOME to compile the code and add NVSHMEM_HOME to LD_LIBRARY_PATH at runtime.

Fixes # (issue)

Type of change

• Documentation change (change only to the documentation, either a fix or a new content)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Infra/Build change
• Code refractor

Changes

Please list the changes introduced in this PR:

• Change A
• Change B

Checklist:

• I have read and followed the contributing guidelines
• The functionality is complete
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes