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>

tests/integration/connection_aware_interface_test.py

@@ -15,7 +15,6 @@ def test_instantiation_fails_when_connect_not_implemented() -> None:
         def disconnect(self) -> None:
             pass
 
-        @property
         def is_connected(self) -> bool:
             return False
 
@@ -32,7 +31,6 @@ def test_instantiation_fails_when_disconnect_not_implemented() -> None:
         def connect(self) -> None:
             pass
 
-        @property
         def is_connected(self) -> bool:
             return False