[Refactor] Unify full-graph parameter update logic (#6041)

### What this PR does / why we need it?

**Refactor: Unify full-graph parameter update logic**

This PR consolidates the scattered full-graph parameter update logic
into a unified approach, improving code architecture and eliminating
duplication.

**Key improvements:**

1. **Unified interface**
- Create `update_full_graph_params` as the single entry point for all
full-graph updates
   - Replace multiple scattered update calls with one unified function
- Remove ~50 lines of duplicated if-else logic across
`model_runner_v1.py` and `eagle_proposer.py`

2. **Better architecture**
- Move update logic to respective Backend classes
(`AscendAttentionBackend`, `AscendMLABackend`)
   - Each Backend manages its own parameter update logic internally
   - Simplify caller code to just dispatch to the appropriate Backend

3. **Cleaner parameter handling**
   - Remove unnecessary `pcp_size` and `dcp_size` parameter passing
   - Get parallel configuration directly from distributed groups
   - Consistent with how other parts of the codebase obtain these values

**Why we need it:**
- **Maintainability**: Future changes only need to be made in one place
per Backend
- **Code quality**: Follows DRY principle and Single Responsibility
Principle
- **Readability**: Cleaner, more intuitive code structure

### Does this PR introduce _any_ user-facing change?

**No.** This is a pure refactoring with no functional changes - same
behavior, cleaner code.

### How was this patch tested?

- All existing unit tests pass with updated mocks
- No new tests needed (pure refactoring, no behavior changes)
- CI validates correctness

---

- vLLM version: v0.13.0

Signed-off-by: lico67373 <918688502@qq.com>
Co-authored-by: drslark <slarksblood@qq.com>
Co-authored-by: weijinqian0 <1184188277@qq.com>

tests/ut/compilation/test_acl_graph.py

@@ -24,12 +24,15 @@ from vllm.forward_context import BatchDescriptor, ForwardContext
 from tests.ut.base import TestBase
 from vllm_ascend.attention.attention_v1 import (AscendMetadata,
                                                 AscendMetadataForDecode)
+from vllm_ascend.attention.context_parallel.attention_cp import \
+    AscendAttentionCPImpl
+from vllm_ascend.attention.context_parallel.mla_cp import AscendMlaCPImpl
 from vllm_ascend.attention.mla_v1 import (AscendMLADecodeMetadata,
                                           AscendMLAMetadata)
 from vllm_ascend.compilation.acl_graph import (
     ACLGraphEntry, ACLGraphWrapper, get_draft_graph_params, get_graph_params,
-    set_draft_graph_params, set_graph_params, update_attn_dcp_pcp_params,
-    update_draft_graph_params_workspaces, update_mla_attn_dcp_pcp_params)
+    set_draft_graph_params, set_graph_params,
+    update_draft_graph_params_workspaces)
 
 
 class TestACLGraphEntry(TestBase):
@@ -811,8 +814,9 @@ class TestPCPDCPGraphParams(TestBase):
              out, lse))
 
         with patch("torch_npu._C._npu_setStream", return_value=None):
-            update_mla_attn_dcp_pcp_params(self.update_stream, forward_context,
-                                           4)
+            AscendMlaCPImpl.update_graph_params(
+                self.update_stream, forward_context, 4
+            )
 
         _mock_graph_task_end.assert_called_once()
 
@@ -852,6 +856,8 @@ class TestPCPDCPGraphParams(TestBase):
              out, lse, 2, 0, 0))
 
         with patch("torch_npu._C._npu_setStream", return_value=None):
-            update_attn_dcp_pcp_params(self.update_stream, forward_context, 4)
+            AscendAttentionCPImpl.update_graph_params(
+                self.update_stream, forward_context, 4, None
+            )
 
         _mock_graph_task_end.assert_called_once()