[PyTorch] Fix: Resolve EP symm-mem window offset for both old and new torch version

[phu0ngng]

Description

Select get_window_offset() or get_offset() at compile time so EP zero-copy builds against PyTorch versions before and after pytorch/pytorch#189088 moved the symm-mem signal pad to the front of the allocation.

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

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

[phu0ngng]

/te-ci L1 torch

[greptile-apps]

Greptile Summary

The PR makes the NCCL symmetric-memory window offset calculation compatible across PyTorch API versions.

• Selects get_window_offset() at compile time when the API is available.
• Falls back to the older get_offset() API while preserving tensor-view storage offsets.

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains.

Important Files Changed

Filename	Overview
transformer_engine/pytorch/csrc/extensions/ep.cpp	Adds compile-time selection between the old and new symmetric-memory offset APIs without changing the surrounding zero-copy window construction flow.

_{Reviews (2): Last reviewed commit: "Merge branch 'main' into fix_pyt_symm" | Re-trigger Greptile}

[phu0ngng]

All EP tests passed. The CI reports the failures FileExistsError: [Errno 17] File exists: '/logs' which is unrelated to this change.

[ptrendx]

/te-ci pytorch