[Fix] Add operations in _dummy_run to maintain synchronization with _process_reqs, resolving a service hang (#2454)

### What this PR does / why we need it?
Fixes hang when batch size < DP size.

### Does this PR introduce _any_ user-facing change?
None.

### How was this patch tested?
After this change, the function in DP case will work now.

- vLLM version: v0.10.1.1
- vLLM main:
d9a55204ba

Signed-off-by: Yizhou Liu <liu_yizhou@outlook.com>

vllm_ascend/worker/model_runner_v1.py

@@ -1911,6 +1911,10 @@ class NPUModelRunner(LoRAModelRunnerMixin):
             )
 
         # Padding for DP
+        num_pad, num_tokens_across_dp_native = self.get_dp_padding(num_tokens)
+        # num_tokens += num_pad  ## Uncomment this after TorchAir is removed
+
+        # Padding for DP (for TorchAir)
         (num_tokens, num_tokens_across_dp, with_prefill,
          _) = self._get_forward_metadata_across_dp_and_pad(
              num_tokens, with_prefill, False)