performance-sliding-window-flash-when-using-flash-attention-with-a-sliding-window-t-a8c8b3d3

THEN In modeling_flash_attention_utils.py, change the window_size assignment from (sliding_window, sliding_window) to (sliding_window - 1, sliding_window) when sliding windows are enabled. This aligns the behavior with the intended sliding window length (including current token) and matches other implementations.

# Before
d_flash_kwargs = {"window_size": (sliding_window, sliding_window)} if use_sliding_windows else {}

# After
d_flash_kwargs = {"window_size": (sliding_window - 1, sliding_window)} if use_sliding_windows else {}