Add isort pre-commit hook, sort imports in src and test directories

tests/test_auto_pilot.py

@@ -1,10 +1,9 @@
+from textual import events
 from textual.app import App
 from textual.pilot import Pilot
-from textual import events
 
 
 def test_auto_pilot() -> None:
-
     keys_pressed: list[str] = []
 
     class TestApp(App):
@@ -12,7 +11,6 @@ def test_auto_pilot() -> None:
             keys_pressed.append(event.key)
 
     async def auto_pilot(pilot: Pilot) -> None:
-
         await pilot.press("tab", *"foo")
         await pilot.exit("bar")