fix(stdio): close stdout on teardown

Author: Epochex

src/mcp/client/stdio.py

@@ -205,6 +205,12 @@ async def stdin_writer():
             except ProcessLookupError:  # pragma: no cover
                 # Process already exited, which is fine
                 pass
+
+            if process.stdout:  # pragma: no branch
+                try:
+                    await process.stdout.aclose()
+                except Exception:  # pragma: no cover
+                    pass
             await read_stream.aclose()
             await write_stream.aclose()
             await read_stream_writer.aclose()