stdlib: fix many attributes which are read-only at runtime but read-write in the stub (#7395)

stdlib/pydoc.pyi

@@ -200,8 +200,10 @@ class Helper:
     symbols: dict[str, str]
     topics: dict[str, str | tuple[str, ...]]
     def __init__(self, input: IO[str] | None = ..., output: IO[str] | None = ...) -> None: ...
-    input: IO[str]
-    output: IO[str]
+    @property
+    def input(self) -> IO[str]: ...
+    @property
+    def output(self) -> IO[str]: ...
     def __call__(self, request: str | Helper | object = ...) -> None: ...
     def interact(self) -> None: ...
     def getline(self, prompt: str) -> str: ...