[feat]decode convert bsnd to tnd and fix bug when pcp and dcp (#3980)

### What this PR does / why we need it?
1、in attention_v1 module, convert bsnd t0 tnd when pcp and dcp
2、fix tochair bug: service startup problem

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

### How was this patch tested?

- vLLM version: v0.11.0
- vLLM main:
83f478bb19

Signed-off-by: weiguihua2 <weiguihua2@huawei.com>

tests/ut/attention/test_attention_v1.py

@@ -63,10 +63,25 @@ class TestAscendAttentionBackend(TestBase):
 
 class TestAscendAttentionMetadataBuilder(TestBase):
 
-    def setUp(self):
+    @patch('vllm.distributed.parallel_state.get_dcp_group')
+    @patch('vllm.distributed.parallel_state._DCP',
+           new_callable=lambda: MagicMock(spec=GroupCoordinator))
+    @patch("vllm.distributed.get_decode_context_model_parallel_world_size",
+           return_value=1)
+    def setUp(self, mock_get_dcp_size, mock_dcp, mock_get_dcp_group):
+        mock_dcp.world_size = 1
+        dcp_group = MagicMock(spec=GroupCoordinator)
+        dcp_group.rank_in_group = 0
+        dcp_group.world_size = 1
+        dcp_group.device_group = MagicMock()
+        mock_get_dcp_group.return_value = dcp_group
+
         self.mock_vllm_config = MagicMock()
         self.mock_vllm_config.model_config.max_model_len = 640
         self.mock_vllm_config.cache_config.block_size = 64
+        self.mock_vllm_config.compilation_config.cudagraph_mode = None
+        self.mock_vllm_config.scheduler_config.max_num_seqs = 10
+        self.mock_vllm_config.scheduler_config.decode_max_num_seqs = 10
         self.mock_device = 'cpu:0'
         self.builder = AscendAttentionMetadataBuilder(None, None,
                                                       self.mock_vllm_config,