Add __all__ to most modules beginning with 'n', 'o' and 'p' (#7345)

stdlib/poplib.pyi

@@ -1,8 +1,14 @@
 import socket
 import ssl
+import sys
 from typing import Any, BinaryIO, NoReturn, Pattern, overload
 from typing_extensions import Literal
 
+if sys.version_info >= (3, 10):
+    __all__ = ["POP3", "error_proto", "POP3_SSL"]
+else:
+    __all__ = ["POP3", "error_proto"]
+
 _LongResp = tuple[bytes, list[bytes], int]
 
 class error_proto(Exception): ...