[BugFix] Enforce C locale for CPU binding subprocess parsing (#8261)

### What this PR does / why we need it?
This PR backports the CPU binding locale normalization fix from #7274 to
`releases/v0.18.0`, including the follow-up review fixes already applied
on `main`.

The change forces `LC_ALL`, `LANG`, and `LC_MESSAGES` to `C` before
spawning subprocesses in `vllm_ascend.cpu_binding.execute_command()`, so
parser-dependent command output stays stable on localized systems. It
also handles `subprocess.TimeoutExpired` by killing the child process
before collecting output, and updates the existing unit tests to keep
command-argument coverage while adding timeout-path coverage.

Fixes #6992

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

Users running CPU binding on non-English OS environments should now get
consistent English subprocess output for parser-dependent commands,
avoiding failures caused by inherited locale settings.

### How was this patch tested?
- Updated the existing unit tests in
`tests/ut/device_allocator/test_cpu_binding.py` to assert the locale
environment, retain command argument coverage, and cover the timeout
cleanup path.
- Attempted to run targeted pytest cases locally, but the pytest
invocation did not complete normally in this environment, so I could not
record a clean passing run here.

Attribution:
- Co-authored-by: stdjhs <1601599324@qq.com>
- Signed-off-by: chenchuw886 <chenchuw@huawei.com>

Signed-off-by: chenchuw886 <chenchuw@huawei.com>
Co-authored-by: chenchuw886 <chenchuw@huawei.com>
Co-authored-by: stdjhs <1601599324@qq.com>

vllm_ascend/cpu_binding.py

@@ -37,8 +37,17 @@ def is_arm_cpu() -> bool:
 
 
 def execute_command(cmd: list[str]) -> tuple[str, int]:
-    with subprocess.Popen(cmd, shell=False, stdout=subprocess.PIPE, stderr=subprocess.PIPE) as p:
-        out, _ = p.communicate(timeout=1000)
+    # Force a C locale so subprocess output remains parseable on localized OSes.
+    env = os.environ.copy()
+    env["LC_ALL"] = "C"
+    env["LANG"] = "C"
+    env["LC_MESSAGES"] = "C"
+    with subprocess.Popen(cmd, shell=False, stdout=subprocess.PIPE, stderr=subprocess.PIPE, env=env) as p:
+        try:
+            out, _ = p.communicate(timeout=1000)
+        except subprocess.TimeoutExpired:
+            p.kill()
+            out, _ = p.communicate()
     return out.decode(), p.returncode