fix: restore success-path server_sock.close() before rpc_thread.join()

PR #568 moved the close entirely to the finally block, but the success-path
close is needed to break the RPC thread out of accept() immediately. Without
it, rpc_thread.join(3) may block for up to 3 seconds if the child process
never connected. The finally-block close remains as a safety net for the
exception/error path (the actual fd leak fix).

tools/code_execution_tool.py

@@ -511,6 +511,7 @@ def execute_code(
         duration = round(time.monotonic() - exec_start, 2)
 
         # Wait for RPC thread to finish
+        server_sock.close()  # break accept() so thread exits promptly
         rpc_thread.join(timeout=3)
 
         # Build response