Align WSL detection helpers

Remove the environment-variable fallback from cuda_python_test_helpers._detect_wsl so the test helper matches cuda.core's /proc-based WSL detection. Add comments to both copies to keep the duplicated implementations synchronized.

Xref: https://github.com/NVIDIA/cuda-python/pull/2118/changes#r3278720224

Author: rwgk

cuda_core/cuda/core/system/_system.pyx

@@ -11,6 +11,8 @@
 CUDA_BINDINGS_NVML_IS_COMPATIBLE: bool
 
 
+# Please keep in sync with the equivalent implementation in
+# cuda_python_test_helpers/cuda_python_test_helpers/__init__.py.
 cdef bint _detect_wsl():
     try:
         with open("/proc/sys/kernel/osrelease") as f:

cuda_python_test_helpers/cuda_python_test_helpers/__init__.py

@@ -15,13 +15,13 @@
 ]
 
 
+# Please keep in sync with the equivalent implementation in
+# cuda_core/cuda/core/system/_system.pyx.
 def _detect_wsl() -> bool:
     data = ""
     with suppress(Exception), open("/proc/sys/kernel/osrelease") as f:
         data = f.read().lower()
-    if "microsoft" in data or "wsl" in data:
-        return True
-    return any(os.environ.get(k) for k in ("WSL_DISTRO_NAME", "WSL_INTEROP"))
+    return "microsoft" in data or "wsl" in data
 
 
 IS_WSL: bool = _detect_wsl()