perf(deepseek_v4): use mx.fast.rms_norm in HyperConnection and HyperHead#16

0xClandestine wants to merge 1 commit intoBlaizzy:pc/add-deepseekv4flash-modelBlaizzy/mlx-lm:pc/add-deepseekv4flash-modelfrom

0xClandestine:phew/optimize-blaizzy-deepseekv4flash0xClandestine/mlx-lm:phew/optimize-blaizzy-deepseekv4flashCopy head branch name to clipboard