[Feature] Support npuhraph_ex backend (#4700)

### What this PR does / why we need it?
We introduced the npugraph_ex backend through the vllm's adaptor
dispatch mechanism to accelerate aclgraph. This solution is based on
torch.compile and uses torchair to optimize the fx.graph. The
performance gains are mainly obtained from the static kernel. We
conducted tests on Qwen3-30B and achieved over 5% performance
optimization.

### Does this PR introduce _any_ user-facing change?
Yes, we add a new switch named"enable_npugraph_ex" in additional_config,
default is False.
We also add an example to show how to register custom replacement pass

### More information about this PR
This feature depends on the release of CANN and torch_npu in Q4. 
We tested it on a package that has not been publicly released yet and
verified that the functionality works.
This feature is still experimental at the moment; setting the config
true will directly raise error.
Merging into the main branch initially involves some preliminary commits
to facilitate subsequent development and testing of the feature, as well
as to avoid submitting an excessively large PR at once.

- vLLM version: v0.12.0
- vLLM main:
ad32e3e19c

---------

Signed-off-by: chencangtao <chencangtao@huawei.com>
Signed-off-by: ChenCangtao <50493711+ChenCangtao@users.noreply.github.com>
Co-authored-by: chencangtao <chencangtao@huawei.com>
Co-authored-by: panchao-hub <315134829@qq.com>
Co-authored-by: wbigat <wbigat@163.com>
Co-authored-by: Mengqing Cao <cmq0113@163.com>

tests/ut/test_ascend_config.py

@@ -57,10 +57,21 @@ class TestAscendConfig(TestBase):
         ascend_config = init_ascend_config(test_vllm_config)
         self.assertEqual(ascend_config.expert_map_path, "test_expert_map_path")
         self.assertTrue(ascend_config.multistream_overlap_shared_expert)
+        self.assertFalse(ascend_config.enable_npugraph_ex)
 
         ascend_compilation_config = ascend_config.ascend_compilation_config
         self.assertFalse(ascend_compilation_config.enable_quantization_fusion)
 
+    @_clean_up_ascend_config
+    def test_init_ascend_config_enable_npugraph_ex(self):
+        with self.assertRaises(NotImplementedError):
+            test_vllm_config = VllmConfig()
+            test_vllm_config.additional_config = {
+                "enable_npugraph_ex": True,
+                "refresh": True,
+            }
+            init_ascend_config(test_vllm_config)
+
     @_clean_up_ascend_config
     def test_get_ascend_config(self):
         test_vllm_config = VllmConfig()