[fea] Add fp32 RMSNorm output for fused qk group quant

[wuhuikx]

Summary

• Add an optional q_out_unquantized_fp32 output to fused_qk_rmsnorm_group_quant so callers can reuse the kernel's internal fp32 RMSNorm result.
• Wire the Python wrapper, pybind binding, C++ declaration, dispatch macros, and kernel store path for the new output while preserving existing call sites.
• Keep per-token quant forwarding compatible by passing std::nullopt for the new optional output.

Performance

Measured with MiniMax-M3-MXFP4 on ATOM using the same aiter build and only toggling the ATOM router path between baseline bf16 norm + .float() and optimized fp32 norm output reuse. Workload: ISL=8000, OSL=1000, TP=4, max_num_seqs=32.

• CON=4: output tok/s 395.33 -> 407.61 (+3.11%), mean TPOT 9.45 -> 9.14 ms (-3.28%)
• CON=8: output tok/s 707.74 -> 745.23 (+5.30%), mean TPOT 10.32 -> 9.97 ms (-3.39%)
• CON=16: output tok/s 1217.98 -> 1254.47 (+3.00%), mean TPOT 12.23 -> 11.99 ms (-1.96%)

Test plan

• python3 -m py_compile aiter/ops/fused_qk_rmsnorm_group_quant.py
• JIT smoke test for fused_qk_rmsnorm_group_quant(..., q_out_unquantized_fp32=...) on CUDA/bf16 input.
• MiniMax-M3 ATOM serving benchmark for CON=4,8,16 with the above workload.

[github-actions]

🏷️ CI Guide

Runs automatically on every PR:

• ✅ Pre-checks (submodule verification, code formatting)
• ✅ Aiter op tests (gfx942 + gfx950)
• ✅ Triton tests on MI35X (only when aiter/ops/triton/** or related paths are changed)

Extended tests (opt-in via labels):

Label	Tests
ci:triton-300x	Run an additional Triton test job on MI300X in PRs; main branch always runs both MI35X and MI300X
ci:sglang	SGLang integration tests: DeepSeek-R1-MXFP4 accuracy, Qwen 3.5 accuracy
ci:atom	ATOM benchmark: DeepSeek-R1-0528, GPT-OSS-120B
ci:atom_full	ATOM accuracy suite for PR and main models from ATOM models_accuracy.json
ci:vllm	vLLM benchmark: GPT-OSS-120B, DeepSeek-R1-0528, Kimi-K2.5
ci:all	All standard extended tests (excludes ci:atom_full)

Only add ci:atom_full for FlyDSL or Triton upgrades.
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