[ROCm] Bump AITER to v0.1.16.post4

[Fangzhou-Ai]

Purpose

Advance the ROCm image build from AITER v0.1.16.post3 to
v0.1.16.post4. This brings the gfx950 MXFP4 MoE path, top-k and
MLA metadata/reduction optimizations, and AITER's FlyDSL 0.2.2 dependency.
FlyDSL does not need a separate vLLM pin because the AITER build stage installs
AITER's requirements.txt before building its wheel.

The tested AITER source commit was
72eedddd921d0fb8f274e7b9291dd04306d089ef.

Duplicate-work check

The required open-PR searches were run for AITER 0.1.16.post4,
AITER FlyDSL, bump aiter, and ROCm AITER; no PR already performs this
dependency uplift. #48581 touches the same Dockerfile for a materially
different gfx942 MQA integration and commit-pinning change; it does not bump
the image to this post4 release.

AI assistance was used to prepare this draft, run the duplicate checks, and
organize the existing benchmark evidence. The human submitter is responsible
for reviewing the one-line diff and validating the evidence before marking the
PR ready.

Test Plan

• Verify the candidate ref and exact commit on ROCm/aiter.
• Run pre-commit on docker/Dockerfile.rocm_base.
• Validate the source-built candidate with Kimi-K2.5-MXFP4 on 4x MI355X:
  TP4/EP1, FP4 weights, FP8 KV cache, ISL/OSL 1024, concurrency 4 and 128.
• Run GSM8K 5-shot through the OpenAI-compatible serving endpoint.

Test Result

• pre-commit run --files docker/Dockerfile.rocm_base: passed.
• Candidate provenance: amd-aiter==0.1.16.post4.dev11+g72eedddd9,
  AITER source 72eedddd921d0fb8f274e7b9291dd04306d089ef,
  flydsl==0.2.2.
• Kimi-K2.5-MXFP4 serving results:

Concurrency	Requests	Total TPUT	TPUT/GPU	Median TTFT	Median TPOT
4	40	942.39 tok/s	235.60 tok/s	111.61 ms	8.144 ms
128	1280	6950.36 tok/s	1737.59 tok/s	211.28 ms	36.545 ms

• GSM8K 5-shot: 1319 samples, strict-match 0.9704, flexible-extract
  0.9704.
• The exact candidate was built from source and exercised by these serving
  runs. A full Docker image build was not repeated locally; CI will validate
  the Docker build path.

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Essential Elements of an Effective PR Description Checklist

• The purpose of the PR is explained.
• The test plan includes the commands and workloads used.
• Test and model-evaluation results are included.
• No documentation update is needed for a dependency-only uplift.

BEFORE SUBMITTING, PLEASE READ https://docs.vllm.ai/en/latest/contributing

[Fangzhou-Ai]

@dllehr-amd @Rohan138 @ChuanLi1101 @tjtanaa @AndreasKaratzas

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