Fix Windows race condition in test_stdio_client_immediate_completion

Add small delay to ensure process doesn't exit before async tasks initialize.
This prevents BrokenResourceError on fast Windows systems.

Author: felixweinberger

tests/client/test_stdio.py

@@ -150,9 +150,10 @@ async def test_stdio_client_immediate_completion():
     when processes exit normally and quickly.
     """
 
-    # Use a Python script that prints and exits immediately
-    # This is more consistent across platforms than echo
-    script_content = "print('hello')"
+    # Use a Python script that prints and exits after a brief moment
+    # This avoids race conditions on fast systems where the process
+    # exits before async tasks are fully initialized
+    script_content = "import time; print('hello'); time.sleep(0.1)"
 
     server_params = StdioServerParameters(
         command=sys.executable,