fix: ensure proper cleanup in stdio_client

Author: hwaxxer

src/mcp/client/stdio.py

@@ -159,4 +159,11 @@ async def stdin_writer():
     ):
         tg.start_soon(stdout_reader)
         tg.start_soon(stdin_writer)
-        yield read_stream, write_stream
+        try:
+            yield read_stream, write_stream
+        finally:
+            for stream in (process.stdin, process.stdout, process.stderr):
+                if stream:
+                    await stream.aclose()
+            process.terminate()
+            await process.aclose()