[PyTorch] torch.compile support for permutation functions

[pggPL]

Description

This PR adds torch.compile(fullgraph=True) support for MoE permutation operations (moe_permute, moe_unpermute, moe_sort_chunks_by_index) by converting all torch.autograd.Function implementations to PyTorch custom operators using torch.library.custom_op.

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