Sync asyncio.isfuture definitions by sharing asyncio.base_futures.isfuture definition (#7353)

stdlib/asyncio/futures.pyi

@@ -2,6 +2,7 @@ import sys
 from _typeshed import Self
 from concurrent.futures._base import Error, Future as _ConcurrentFuture
 from typing import Any, Awaitable, Callable, Generator, Iterable, TypeVar
+from typing_extensions import TypeGuard
 
 from .events import AbstractEventLoop
 
@@ -25,6 +26,11 @@ else:
 
 _T = TypeVar("_T")
 
+# asyncio defines 'isfuture()' in base_futures.py and re-imports it in futures.py
+# but it leads to circular import error in pytype tool.
+# That's why the import order is reversed.
+def isfuture(obj: object) -> TypeGuard[Future[Any]]: ...
+
 if sys.version_info < (3, 7):
     class _TracebackLogger:
         exc: BaseException
@@ -34,8 +40,6 @@ if sys.version_info < (3, 7):
         def clear(self) -> None: ...
         def __del__(self) -> None: ...
 
-def isfuture(obj: object) -> bool: ...
-
 class Future(Awaitable[_T], Iterable[_T]):
     _state: str
     _exception: BaseException