use stdlib instead of backports after 3.8

Summary:
Later was built on backports from 3.8 to give us features even while using 3.7.
When we moved to 3.8 we kept them because I wasn't exactly sure at the time that all the fixes we baked into 3.8 async_mock had made it into the stdlib 3.8 yet.

Well if the version of python is greater than 3.8 lets just use the stdlib

Bumping version so we can release to pypi

Differential Revision: D43885595

fbshipit-source-id: d5e1ca89984b818c512cea48e9dee0ebc9040b3a

later/__init__.py

@@ -18,7 +18,7 @@
 from .task import as_task, cancel, START_TASK, Watcher, WatcherError
 
 
-__version__ = "22.11.1"
+__version__ = "23.03.1"
 __all__ = [
     "BiDirectionalEvent",
     "START_TASK",

later/unittest/case.py

@@ -28,7 +28,11 @@
 from functools import wraps
 from typing import Any, Callable, TypeVar
 
-from .backport.async_case import IsolatedAsyncioTestCase as AsyncioTestCase
+
+if sys.version_info[:2] >= (3, 9):  # pragma: nocover
+    from unittest import IsolatedAsyncioTestCase as AsyncioTestCase
+else:  # pragma: nocover
+    from .backport.async_case import IsolatedAsyncioTestCase as AsyncioTestCase
 
 
 _F = TypeVar("_F", bound=Callable[..., Any])

later/unittest/mock.py

@@ -13,10 +13,15 @@
 # under the License.
 from __future__ import annotations
 
+import sys
+
 from typing import Any
 from unittest.mock import call, DEFAULT
 
-from .backport.mock import AsyncMock, create_autospec, MagicMock, Mock, patch
+if sys.version_info >= (3, 9):  # pragma: nocover
+    from unittest.mock import AsyncMock, create_autospec, MagicMock, Mock, patch
+else:  # pragma: nocover
+    from .backport.mock import AsyncMock, create_autospec, MagicMock, Mock, patch
 
 
 __all__ = [