[main] flashcomm_v1 optim in Qwen Dense Models (#2802)

### What this PR does / why we need it?
Flashcomm_v1 optim in Qwen Dense Models.

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

### How was this patch tested?
CI passed with new added/existing test.

- vLLM version: v0.10.1.1
- vLLM main:
5e537f45b4

Co-authored-by: 1024daniel <xxltju324@gmail.com>

vllm_ascend/envs.py

@@ -131,6 +131,15 @@ env_variables: Dict[str, Callable[[], Any]] = {
     # this feature is supported in A2, and eager mode will get better performance.
     "VLLM_ASCEND_ENABLE_MATMUL_ALLREDUCE":
     lambda: bool(int(os.getenv("VLLM_ASCEND_ENABLE_MATMUL_ALLREDUCE", '0'))),
+    # Whether to enable FlashComm optimization when tensor parallel is enabled.
+    # This feature will get better performance when concurrency is large.
+    "VLLM_ASCEND_ENABLE_FLASHCOMM":
+    lambda: bool(int(os.getenv("VLLM_ASCEND_ENABLE_FLASHCOMM", '0'))),
+    # Whether to enable dense model and general optimizations for better performance.
+    # Since we modified the base parent class `linear`, this optimization is also applicable to other model types.
+    # However, there might be hidden issues, and it is currently recommended to prioritize its use with dense models.
+    "VLLM_ASCEND_ENABLE_DENSE_OPTIMIZE":
+    lambda: bool(int(os.getenv("VLLM_ASCEND_ENABLE_DENSE_OPTIMIZE", '0'))),
     # Whether to enable mlp optimize when tensor parallel is enabled.
     # this feature in eager mode will get better performance.
     "VLLM_ASCEND_ENABLE_MLP_OPTIMIZE":