asyncio: make AbstractServer abstract and remove unnecessary metaclass=ABCMeta (#7185)

Author: AlexWaygood

stdlib/asyncio/base_events.pyi

@@ -1,7 +1,6 @@
 import ssl
 import sys
 from _typeshed import FileDescriptorLike
-from abc import ABCMeta
 from asyncio.events import AbstractEventLoop, AbstractServer, Handle, TimerHandle
 from asyncio.futures import Future
 from asyncio.protocols import BaseProtocol
@@ -33,6 +32,10 @@ class Server(AbstractServer):
             backlog: int,
             ssl_handshake_timeout: float | None,
         ) -> None: ...
+        def get_loop(self) -> AbstractEventLoop: ...
+        def is_serving(self) -> bool: ...
+        async def start_serving(self) -> None: ...
+        async def serve_forever(self) -> None: ...
     else:
         def __init__(self, loop: AbstractEventLoop, sockets: list[socket]) -> None: ...
     if sys.version_info >= (3, 8):
@@ -43,8 +46,10 @@ class Server(AbstractServer):
         def sockets(self) -> list[socket]: ...
     else:
         sockets: list[socket] | None
+    def close(self) -> None: ...
+    async def wait_closed(self) -> None: ...
 
-class BaseEventLoop(AbstractEventLoop, metaclass=ABCMeta):
+class BaseEventLoop(AbstractEventLoop):
     def run_forever(self) -> None: ...
     # Can't use a union, see mypy issue  # 1873.
     @overload

stdlib/asyncio/events.pyi

@@ -56,18 +56,24 @@ class TimerHandle(Handle):
         def when(self) -> float: ...
 
 class AbstractServer:
+    @abstractmethod
     def close(self) -> None: ...
     if sys.version_info >= (3, 7):
         async def __aenter__(self: Self) -> Self: ...
         async def __aexit__(self, *exc: Any) -> None: ...
+        @abstractmethod
         def get_loop(self) -> AbstractEventLoop: ...
+        @abstractmethod
         def is_serving(self) -> bool: ...
+        @abstractmethod
         async def start_serving(self) -> None: ...
+        @abstractmethod
         async def serve_forever(self) -> None: ...
 
+    @abstractmethod
     async def wait_closed(self) -> None: ...
 
-class AbstractEventLoop(metaclass=ABCMeta):
+class AbstractEventLoop:
     slow_callback_duration: float
     @abstractmethod
     def run_forever(self) -> None: ...
@@ -491,7 +497,7 @@ class AbstractEventLoop(metaclass=ABCMeta):
         @abstractmethod
         async def shutdown_default_executor(self) -> None: ...
 
-class AbstractEventLoopPolicy(metaclass=ABCMeta):
+class AbstractEventLoopPolicy:
     @abstractmethod
     def get_event_loop(self) -> AbstractEventLoop: ...
     @abstractmethod