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

stdlib/numbers.pyi

@@ -4,6 +4,8 @@
 from abc import ABCMeta, abstractmethod
 from typing import Any, SupportsFloat, overload
 
+__all__ = ["Number", "Complex", "Real", "Rational", "Integral"]
+
 class Number(metaclass=ABCMeta):
     @abstractmethod
     def __hash__(self) -> int: ...