[ROCm][Critical] Fix the GDN import bug

[tjtanaa]

Purpose

#41126 changes the import of gdn thus causing import error. However this import error is critical as it will cause the server to crashed when we use VLLM_ROCM_USE_AITER=1

(EngineCore pid=2818) ERROR 05-23 13:50:24 [core.py:1165]     self.aot_compiled_fn = self.aot_compile(*args, **kwargs)
(EngineCore pid=2818) ERROR 05-23 13:50:24 [core.py:1165]                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
(EngineCore pid=2818) ERROR 05-23 13:50:24 [core.py:1165]   File "/usr/local/lib/python3.12/dist-packages/vllm/compilation/wrapper.py", line 167, in aot_compile
(EngineCore pid=2818) ERROR 05-23 13:50:24 [core.py:1165]     return self._compiled_callable.aot_compile((args, kwargs))
(EngineCore pid=2818) ERROR 05-23 13:50:24 [core.py:1165]            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
(EngineCore pid=2818) ERROR 05-23 13:50:24 [core.py:1165]   File "/usr/local/lib/python3.12/dist-packages/torch/_dynamo/eval_frame.py", line 832, in aot_compile
(EngineCore pid=2818) ERROR 05-23 13:50:24 [core.py:1165]     return aot_compile_fullgraph(
(EngineCore pid=2818) ERROR 05-23 13:50:24 [core.py:1165]            ^^^^^^^^^^^^^^^^^^^^^^
(EngineCore pid=2818) ERROR 05-23 13:50:24 [core.py:1165]   File "/usr/local/lib/python3.12/dist-packages/torch/_dynamo/aot_compile.py", line 239, in aot_compile_fullgraph
(EngineCore pid=2818) ERROR 05-23 13:50:24 [core.py:1165]     compiled_fn = backend(
(EngineCore pid=2818) ERROR 05-23 13:50:24 [core.py:1165]                   ^^^^^^^^
(EngineCore pid=2818) ERROR 05-23 13:50:24 [core.py:1165]   File "/usr/local/lib/python3.12/dist-packages/torch/__init__.py", line 2509, in __call__
(EngineCore pid=2818) ERROR 05-23 13:50:24 [core.py:1165]     return self.compiler_fn(model_, inputs_, **self.kwargs)
(EngineCore pid=2818) ERROR 05-23 13:50:24 [core.py:1165]            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
(EngineCore pid=2818) ERROR 05-23 13:50:24 [core.py:1165]   File "/usr/lib/python3.12/contextlib.py", line 81, in inner
(EngineCore pid=2818) ERROR 05-23 13:50:24 [core.py:1165]     return func(*args, **kwds)
(EngineCore pid=2818) ERROR 05-23 13:50:24 [core.py:1165]            ^^^^^^^^^^^^^^^^^^^
(EngineCore pid=2818) ERROR 05-23 13:50:24 [core.py:1165]   File "/usr/local/lib/python3.12/dist-packages/vllm/compilation/backends.py", line 1163, in __call__
(EngineCore pid=2818) ERROR 05-23 13:50:24 [core.py:1165]     self.configure_post_pass()
(EngineCore pid=2818) ERROR 05-23 13:50:24 [core.py:1165]   File "/usr/local/lib/python3.12/dist-packages/vllm/compilation/backends.py", line 948, in configure_post_pass
(EngineCore pid=2818) ERROR 05-23 13:50:24 [core.py:1165]     self.pass_manager.configure(self.vllm_config)
(EngineCore pid=2818) ERROR 05-23 13:50:24 [core.py:1165]   File "/usr/local/lib/python3.12/dist-packages/vllm/compilation/passes/pass_manager.py", line 163, in configure
(EngineCore pid=2818) ERROR 05-23 13:50:24 [core.py:1165]     RocmAiterRMSNormQuantFusionPass(config),
(EngineCore pid=2818) ERROR 05-23 13:50:24 [core.py:1165]     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
(EngineCore pid=2818) ERROR 05-23 13:50:24 [core.py:1165]   File "/usr/local/lib/python3.12/dist-packages/vllm/compilation/passes/inductor_pass.py", line 139, in fn_new
(EngineCore pid=2818) ERROR 05-23 13:50:24 [core.py:1165]     result = fn(*args, **kwargs)
(EngineCore pid=2818) ERROR 05-23 13:50:24 [core.py:1165]              ^^^^^^^^^^^^^^^^^^^
(EngineCore pid=2818) ERROR 05-23 13:50:24 [core.py:1165]   File "/usr/local/lib/python3.12/dist-packages/vllm/compilation/passes/fusion/rocm_aiter_fusion.py", line 563, in __init__
(EngineCore pid=2818) ERROR 05-23 13:50:24 [core.py:1165]     from vllm.model_executor.layers.mamba.gdn_linear_attn import (
(EngineCore pid=2818) ERROR 05-23 13:50:24 [core.py:1165] ModuleNotFoundError: No module named 'vllm.model_executor.layers.mamba.gdn_linear_attn'

Test Plan

1. fix unit test pytest -svvvv tests/compile/passes/test_fusion.py::test_aiter_fusion_rmsnorm_gated_quant

2. Evaluate that the following command works and model generate correct end to end accuracy

#!/bin/bash

rm -rf ~/.cache/vllm
export VLLM_ROCM_USE_AITER=1

vllm serve Qwen/Qwen3-Next-80B-A3B-Instruct-FP8 \
  --compilation-config '{"cudagraph_mode":"FULL_AND_PIECEWISE","custom_ops":["-rms_norm","-silu_and_mul","+quant_fp8"],"pass_config":{"fuse_norm_quant":true}}'

Test Result

1. pytest -svvvv tests/compile/passes/test_fusion.py::test_aiter_fusion_rmsnorm_gated_quant

======================= 2 passed, 21 warnings in 11.54s ========================

2. Acc of Qwen/Qwen3-Next-80B-A3B-Instruct-FP8

local-completions ({'model': 'Qwen/Qwen3-Next-80B-A3B-Instruct-FP8', 'base_url': 'http://0.0.0.0:8000/v1/completions', 'num_concurrent': 256, 'max_retries': 10, 'max_gen_toks': 2048, 'max_length': 1048576, 'timeout': 60000}), gen_kwargs: ({}), limit: None, num_fewshot: 8, batch_size: auto
|Tasks|Version|     Filter     |n-shot|  Metric   |   |Value |   |Stderr|
|-----|------:|----------------|-----:|-----------|---|-----:|---|-----:|
|gsm8k|      3|flexible-extract|     8|exact_match|↑  |0.9507|±  |0.0060|
|     |       |strict-match    |     8|exact_match|↑  |0.9431|±  |0.0064|

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Essential Elements of an Effective PR Description Checklist

• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• The test plan, such as providing test command.
• The test results, such as pasting the results comparison before and after, or e2e results
• (Optional) The necessary documentation update, such as updating supported_models.md and examples for a new model.

[tjtanaa]

@tpopp Please evaluate if your optimization in #40710 is still working after Mamba Refactoring #41126 .

This PR is needed as quick critical fix as it affects all models when AITER is used.

[gemini-code-assist]

Code Review

This pull request updates the import path for GatedDeltaNetAttention to its new location in vllm.model_executor.layers.mamba.gdn.base within the ROCm Aiter fusion pass and the fusion test suite. It also adds a type ignore annotation to handle type-checking issues during layer discovery. I have no feedback to provide as the existing review comments were purely explanatory and did not identify any issues.