Apply pa_gluon for aiter_backend

[apinge]

Motivation

In this PR, I applied torch.ops.aiter.pa_decode_gluon for aiter_backend. In order to match the new layout, the MHA prefill must be changed to flash_attn_varlen_func and some extra triton kernels added.

For some old triton version, there will be compliation issues, pls apply this patch apinge/aiter@3687fb5 to the aiter.

Modifications

Accuracy Tests

# FP8 TP2
> python3 sglang/benchmark/gsm8k/bench_sglang.py --port 9080 --enable-thinking --tokenizer-path /models/Qwen3.5-27B-PTPC-compressor --max-new-tokens 4096                                                                                                                        
100%|███████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████| 200/200 [08:46<00:00,  2.63s/it]
Accuracy: 0.750
Invalid: 0.010
Latency: 526.365 s
Output throughput: 527.392 token/s
# BF16 TP2
>python3 sglang/benchmark/gsm8k/bench_sglang.py --port 9080 --enable-thinking --tokenizer-path /models/Qwen3.5-27B --max-new-tokens 4096
100%|███████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████████| 200/200 [03:37<00:00,  1.09s/it]
Accuracy: 0.820
Invalid: 0.005
Latency: 217.747 s
Output throughput: 1326.462 token/s

Benchmarking and Profiling

Checklist

• Format your code according to the Format code with pre-commit.
• Add unit tests according to the Run and add unit tests.
• Update documentation according to Write documentations.
• Provide accuracy and speed benchmark results according to Test the accuracy and Benchmark the speed.
• Follow the SGLang code style guidance.

Review Process

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2. Get approvals from CODEOWNERS and other reviewers.
3. Trigger CI tests with comments or contact authorized users to do so.
   • /tag-run-ci-label, /rerun-failed-ci, /tag-and-rerun-ci
4. After green CI and required approvals, ask Merge Oncalls to merge.