[Bugfix] Fix the Eagle3 inference failure issue. (#4721)

### What this PR does / why we need it?
Fix the Eagle3 inference failure issue.
error message: "EngineCore encountered an issue. See stack trace (above)
for the root cause."

Fixes https://github.com/vllm-project/vllm-ascend/issues/4323

### How was this patch tested?
`vllm serve /nfs/1_AscendPackage/05_weights_public/Qwen3-32B \
--served-model-name Qwen3-32B \ -tp 4 \ --host "0.0.0.0" \ --port "8000"
\ --trust-remote-code \ --speculative-config
'{"method":"eagle3","model":"/home/scd/qwen3_32b_eagle3/","num_speculative_tokens":4,"draft_tensor_parallel_size":1}'
\ --max-num-batched-tokens 4096 \ --max-model-len 4096`

```
curl http://localhost:8000/v1/completions \
    -H "Content-Type: application/json" \
    -d '{
        "model": "Qwen3-32B",
        "prompt": "hi, where is the capital of France?",
        "max_tokens": 10,
        "temperature": 0
    }' | python3 -m json.tool
```

vLLM version: v0.11.0
vLLM-ascend version: v0.11.0rc2

Signed-off-by: 17764591921 <sunchend@outlook.com>

vllm_ascend/utils.py

@@ -61,6 +61,7 @@ _IS_VL_MODEL = None
 _ENABLE_SP = None
 _HAS_LAYER_IDX = None
 _ENABLE_NZ = None
+_IS_EAGLE_MODE = None
 
 
 def is_310p():
@@ -73,14 +74,20 @@ def is_310p():
 
 def is_enable_nz(dtype: Optional[torch.dtype] = torch.int8,
                  vllm_config: Optional[VllmConfig] = None) -> bool:
-    global _ENABLE_NZ
+    global _ENABLE_NZ, _IS_EAGLE_MODE
     if _ENABLE_NZ is None:
         if not vllm_config:
             raise ValueError(
                 "vllm_config must be provided when _ENABLE_NZ is None")
         _ENABLE_NZ = envs_ascend.VLLM_ASCEND_ENABLE_NZ and vllm_config.model_config.hf_config.model_type != "qwen3_next"
+
+        _IS_EAGLE_MODE = (
+            vllm_config.speculative_config is not None and 
+            getattr(vllm_config.speculative_config, 'method', None) in ("eagle", "eagle3")
+        )
+
     if dtype in [torch.float16, torch.bfloat16]:
-        return False
+        return _ENABLE_NZ if _IS_EAGLE_MODE else False
     return _ENABLE_NZ