fix(dsv4): follow AITER FP4 MQA package move

[yhl-amd]

Summary

• update all DeepSeek V4 FP4 MQA decode and prefill imports to the current AITER kernels.mqa_logits package
• cover both attention-metadata scheduling and model scorer call sites
• add a CPU-only AST contract test that rejects stale or unexpected FP4 MQA import paths

Context

ROCm/aiter#4609 moved pa_mqa_logits_fp4.py and pa_mqa_logits_fp4_prefill.py under aiter.ops.flydsl.kernels.mqa_logits. ATOM nightly images build AITER from HEAD, while these six lazy imports still referenced the removed flat paths.

DeepSeek V4 on gfx950 with --index-cache-dtype fp4 therefore fails during model warmup with:

ModuleNotFoundError: No module named 'aiter.ops.flydsl.kernels.pa_mqa_logits_fp4_prefill'

The move retained all five APIs used by ATOM, so no call-site or kernel behavior changes are required.

AITER move: ROCm/aiter#4609
Observed failure: https://github.com/SemiAnalysisAI/InferenceX/actions/runs/32338825624/job/96333731386#step:4:1091

Validation

• executed the new AST import-contract test with Python 3.12
• compiled both changed production modules and the new test with compileall
• ran git diff --check
• verified the five imported symbols are present in the current AITER modules

No GPU workload was run for this import-only change.

[github-actions]

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