stdlib: Add many missing dunder overrides (#7231)

stdlib/multiprocessing/managers.pyi

@@ -1,7 +1,8 @@
 import queue
 import sys
 import threading
-from contextlib import AbstractContextManager
+from _typeshed import Self
+from types import TracebackType
 from typing import Any, AnyStr, Callable, Generic, Iterable, Mapping, Sequence, TypeVar
 
 from .connection import Connection
@@ -69,7 +70,7 @@ class Server:
     def serve_forever(self) -> None: ...
     def accept_connection(self, c: Connection, name: str) -> None: ...
 
-class BaseManager(AbstractContextManager[BaseManager]):
+class BaseManager:
     def __init__(
         self, address: Any | None = ..., authkey: bytes | None = ..., serializer: str = ..., ctx: BaseContext | None = ...
     ) -> None: ...
@@ -90,12 +91,14 @@ class BaseManager(AbstractContextManager[BaseManager]):
         method_to_typeid: Mapping[str, str] | None = ...,
         create_method: bool = ...,
     ) -> None: ...
+    def __enter__(self: Self) -> Self: ...
+    def __exit__(self, exc_type: type[BaseException], exc_val: BaseException, exc_tb: TracebackType) -> None: ...
 
 # Conflicts with method names
 _dict = dict
 _list = list
 
-class SyncManager(BaseManager, AbstractContextManager[SyncManager]):
+class SyncManager(BaseManager):
     def BoundedSemaphore(self, value: Any = ...) -> threading.BoundedSemaphore: ...
     def Condition(self, lock: Any = ...) -> threading.Condition: ...
     def Event(self) -> threading.Event: ...