Fix cuDNN sliding window size

[cyanguwa]

Description

This PR adjusts the sliding window size in FusedAttention (cuDNN attention) so it's consistent with our support in FlashAttention and UnfusedDotProductAttention.

cuDNN supports sliding window (i - window_size_left, i], exclusive of the i -window_size_left element. By passing window_size_left + 1 to cuDNN, we achieve the same effect as the [i - window_size_left, i] support.

This PR also reduces the window size in our unit tests so any numerical differences between backends will be easier to notice.

Fixes #1197

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:

• Adjust the window_size passed to cuDNN
• Test smaller window sizes in unit tests

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

[cyanguwa]

/te-ci pytorch

[cyanguwa]

/te-ci pytorch

[ksivaman]

Makes sense, LGTM!

[ksivaman]

/te-ci pytorch