Implement a __eq__ method for _power_managing.Proposal

Earlier a default `eq` implementation was conflicting with the custom
`lt` implementation on what properties were used to compare two
proposals.

Signed-off-by: Sahas Subramanian <[email protected]>

Author: shsms

src/frequenz/sdk/actor/_power_managing/_base_classes.py

@@ -231,6 +231,27 @@ def __lt__(self, other: Proposal) -> bool:
             self.priority == other.priority and self.source_id < other.source_id
         )
 
+    def __eq__(self, other: object) -> bool:
+        """Check if two proposals are equal.
+
+        Equality is determined by the priority and source ID of the proposals, so
+        two proposals are equal if they have the same priority and source ID, even
+        if they have different power values or creation times.
+
+        This is so that there is only one active proposal for each actor in the bucket,
+        and older proposals are replaced by newer ones.
+
+        Args:
+            other: The other proposal to compare to.
+
+        Returns:
+            Whether the two proposals are equal.
+        """
+        if not isinstance(other, Proposal):
+            return NotImplemented
+
+        return self.priority == other.priority and self.source_id == other.source_id
+
 
 class Algorithm(enum.Enum):
     """The available algorithms for the power manager."""