Qwen3.5 Support

[lucasjinreal]

Hi, Qwen3.5 now native multimodal, and extremly nice on text abilities. Very suitable for local Agents. would consider support

[alan890104]

Really need Qwen3.5 model!!!

[alan890104]

I tried implementing my own 4-bit quantized version to run locally, but it seems I misconfigured something, as the output is meaningless.

[lucasjinreal]

consider add a PR once you get it work..

[woodRock]

I've got it working, but it is very slow, likely needs a custom kernel for the Fused Parallel Scan.

See: #3396