Draft: Use fused push_send_recv kernel for TP AG and RS overlaps

[erhoo82]

Description

Use a single fused sentinel kernel for send and recv signaling.
Set NVTE_UB_FUSED_SEND_RECV=1 to use the fused kernel.

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

• Add the execution path with fused push_send and push_recv for split TP comm overlap kernel with send/recv

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