feat: Add a live property to Download

This property calls `self.update()`, and then returns `self`.
This allows to call `download.live.progress` to get
the progress in real-time for example.

src/aria2p/downloads.py

@@ -212,6 +212,11 @@ def update(self) -> None:
         self._following = None
         self._belongs_to = None
 
+    @property
+    def live(self):
+        self.update()
+        return self
+
     @property
     def name(self):
         """