[Question] Support head_dim=256 for attention ops (Qwen3.5/3.6-style GDN-hybrid models) ？

[yaofeino1]

• The attention ops currently support only head_dim = 80 / 128.Could head_dim=256 be added?

• Recent GDN-hybrid models (Qwen3.5 / 3.6) use head_dim=256 in their full-attention layers, so this would unblock those configs.

• One question: since GDN (linear-attention) layers dominate these models,how much end-to-end latency benefit can we realistically expect from optimizing the full-attention op here? Has anyone benchmarked hpc_ops attention on a Qwen3.5/3.6-class model?

• Happy to help test if a branch is available.