Add BufferedProtocol.eof_received() (#7043)

stdlib/asyncio/protocols.pyi

@@ -15,6 +15,7 @@ if sys.version_info >= (3, 7):
     class BufferedProtocol(BaseProtocol):
         def get_buffer(self, sizehint: int) -> bytearray: ...
         def buffer_updated(self, nbytes: int) -> None: ...
+        def eof_received(self) -> bool | None: ...
 
 class DatagramProtocol(BaseProtocol):
     def connection_made(self, transport: transports.DatagramTransport) -> None: ...  # type: ignore[override]