Strengthen is_connected with cached health probes.

Convert is_connected to a method that verifies backend liveness via TTL-cached ping (Redis) or bucket_exists (MinIO), with cache invalidation on connect/disconnect.

Co-authored-by: Cursor <cursoragent@cursor.com>

python_repositories/interfaces/connection_aware_interface.py

@@ -16,8 +16,10 @@ class ConnectionAwareInterface(ABC):
         """Disconnect from resource."""
         ...
 
-    @property
     @abstractmethod
     def is_connected(self) -> bool:
-        """Check if connected to resource."""
+        """Return whether the adapter has an active, reachable connection.
+
+        Implementations may perform a cached network probe to verify liveness.
+        """
         ...