Add aiter attention support in prefill-attention-backend of gpt-oss#18282

HaiShaw merged 3 commits intosgl-project:mainsgl-project/sglang:mainfrom

HaiShaw:gpt-oss-with-aiter-prefill-swaHaiShaw/sglang:gpt-oss-with-aiter-prefill-swaCopy head branch name to clipboard