gh-78889: Stop IDLE Shell freezes from sys.stdout.shell.xyz (#121876)

Problem occurred when attribute xyz could not be pickled.
Since this is not trivial to selectively fix, block all
attributes (other than 'width').  IDLE does not access them
and they are private implementation details.

Lib/idlelib/run.py

@@ -443,6 +443,9 @@ class StdioFile(io.TextIOBase):
 
     def __init__(self, shell, tags, encoding='utf-8', errors='strict'):
         self.shell = shell
+        # GH-78889: accessing unpickleable attributes freezes Shell.
+        # IDLE only needs methods; allow 'width' for possible use.
+        self.shell._RPCProxy__attributes = {'width': 1}
         self.tags = tags
         self._encoding = encoding
         self._errors = errors