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

tests/test_screens.py

@@ -16,15 +16,17 @@ async def test_installed_screens():
         SCREENS = {
             "home": Screen,  # Screen type
             "one": Screen(),  # Screen instance
-            "two": lambda: Screen()  # Callable[[], Screen]
+            "two": lambda: Screen(),  # Callable[[], Screen]
         }
 
     app = ScreensApp()
     async with app.run_test() as pilot:
         pilot.app.push_screen("home")  # Instantiates and pushes the "home" screen
-        pilot.app.push_screen("one")   # Pushes the pre-instantiated "one" screen
+        pilot.app.push_screen("one")  # Pushes the pre-instantiated "one" screen
         pilot.app.push_screen("home")  # Pushes the single instance of "home" screen
-        pilot.app.push_screen("two")   # Calls the callable, pushes returned Screen instance
+        pilot.app.push_screen(
+            "two"
+        )  # Calls the callable, pushes returned Screen instance
 
         assert len(app.screen_stack) == 5
         assert app.screen_stack[1] is app.screen_stack[3]
@@ -40,10 +42,8 @@ async def test_installed_screens():
             pilot.app.pop_screen()
 
 
-
 @skip_py310
 async def test_screens():
-
     app = App()
     app._set_active()