Implement a fused RMSNorm + SiLU gate kernel for Qwen3.5 models

Implement a fused RMSNorm + SiLU gate kernel for Qwen3.5 models: a task in LegoFlow-SWE (Harbor dataset). Currently these three steps are executed as separate eager operations, which is slow and memory‑intensive – especially for large hidden sizes and during training where many intermediate…