[Perf] Delete redundant operations in model_runner and forward_context (#3677)

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

Remove redundant operations from `model_runner` and `forward_context`.
This optimization can significantly reduce the idle time (bubble) before
decoding when running models with small parameter counts (e.g.,
Qwen/Qwen2.5-0.5B).

Testing on 800I A2, bubble is reduced from 3.8ms to 2.8ms :
Before
<img width="1655" height="696" alt="image"
src="https://github.com/user-attachments/assets/d7608e52-2438-46dd-8fc9-391fd6274495"
/>

After
<img width="1607" height="774" alt="image"
src="https://github.com/user-attachments/assets/56daf081-2dba-4d2e-99d4-e055187d9806"
/>

### Does this PR introduce _any_ user-facing change?
No

### How was this patch tested?


- vLLM version: v0.11.0rc3
- vLLM main:
https://github.com/vllm-project/vllm/commit/releases/v0.11.1

---------

Signed-off-by: realliujiaxu <realliujiaxu@163.com>

tests/ut/worker/test_model_runner_v1.py

@@ -68,6 +68,8 @@ def test_select_moe_comm_method(soc_version, enable_expert_parallel,
     with patch('vllm_ascend.worker.model_runner_v1.get_ascend_soc_version',
                return_value=soc_version), \
          patch('vllm_ascend.worker.model_runner_v1.is_global_first_rank',
+               return_value=True), \
+         patch('vllm_ascend.worker.model_runner_v1.is_moe_model',
                return_value=True):
 
         # Bind the real method to the mock object
@@ -102,6 +104,8 @@ def test_select_moe_comm_method_unsupported_soc():
                return_value=unsupported_soc), \
          patch('vllm_ascend.worker.model_runner_v1.is_global_first_rank',
                return_value=True), \
+         patch('vllm_ascend.worker.model_runner_v1.is_moe_model',
+                  return_value=True), \
          pytest.raises(ValueError, match=f"Unsupported soc_version: {unsupported_soc}"):
 
         NPUModelRunner._select_moe_comm_method(mock_runner, 100, False)