[Knight-of-Thunder]

Description

To make the computation and communication become overlap, we create a new stream for communication.
To use NVSHMEM APIs easier, and make the code cleaner, we use NVSHMEM pybindings to replace original cpp code.

• For this reason, we need to install nvshmem4py pip install nvshmem4py-cu12, or pip install nvshmem4py-cu13

Nsys profile result:

The orange part is the commucation timeline which is a p2p memcpy of NVSHMEM, the blue part is the computation timeline include flash fwd kernel.

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 refactoring

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