E2E support for Qwen3 dense; fused QK-RMSNorm + RoPE kernel #210

Currently, Qwen3 dense (0.6B-32B) isn't implemented, despite support for Qwen2 and Qwen3.5. Implementation itself would match almost perfectly onto existing ops (similar to Qwen2), with an additional per-head QK-RMSNorm.

I plan to approach this in 2 PRs:

1. Integrating Qwen3 using existing ops, with the same shape as the Qwen2 implementation (alongside a Qwen3RMSNorm covering q_norm and k_norm).
2. Fuse q norm, k norm, and RoPE into one fused_qk_norm_rope kernel that is GQA-aware. I'd implement it as a core op, following the existing _rope_kernel tiling and containing params to apply the general op to all supported models that can use it (Qwen3, Gemma3, Qwen3.5).

I'll be developing on my 3060ti with sm_86.

Some quick questions:

• Anything already being worked on internally for Qwen3 dense?
• Qwen3.5 already uses apply_tilegym_kernel_to_qwen3. Should I name the new one with _qwen3_dense, or rename the old one?
• Does fused kernel fit as a core op, since its reusable accross Gemma3/Qwen3.5, or should I keep it local to Qwen3?