feat: add timeout method for ui.notification (#4444)

This PR is based on #4437 , which explores a way to make notifications
dismiss after a certain period of time.

This PR provides a method called `timeout` that allows people to
directly override the value of timeout (instead of manually modifying
the value of the props)

I did a simple test.It worked well.
```python
# notification.py (This PR did)
class Notification(Element, component='notification.js'):
    ...
    @Property
    def timeout(self) -> Optional[float]:
        """The timout value of the notification."""
        return self._props['options']['timeout']

    @timeout.setter
    def timeout(self,value: Optional[float]) -> None:
        self._props["options"]["timeout"] = (value or 0) *1000
        self.update()

# test.py
import asyncio

from nicegui import ui

async def test_set_timeout():
    n = ui.notification("Test Notification",timeout=None)
    n.on_dismiss(lambda:print("Notification Dismiss."))
    await asyncio.sleep(3)
    n.message="Test Done"
    n.timeout = 3 # This is a new method

ui.button("Test").on_click(test_set_timeout)

ui.run()
```
That's all.

If you have any suggestions for changes to this PR, please let me know.
Thanks a lot.

---------

Co-authored-by: Falko Schindler <[email protected]>

Author: weinibuliu

nicegui/elements/notification.py

@@ -177,6 +177,19 @@ def spinner(self, value: bool) -> None:
         self._props['options']['spinner'] = value
         self.update()
 
+    @property
+    def timeout(self) -> float:
+        """Timeout of the notification in seconds.
+
+        *Added in version 2.13.0*
+        """
+        return self._props['options']['timeout'] / 1000
+
+    @timeout.setter
+    def timeout(self, value: Optional[float]) -> None:
+        self._props['options']['timeout'] = (value or 0) * 1000
+        self.update()
+
     @property
     def close_button(self) -> Union[bool, str]:
         """Whether the notification has a close button."""