refactor: log silent AttributeError catches, add _sync_class to remaining services, drop dead ctx slot

src/distributed_job_manager.py

@@ -24,6 +24,11 @@ logger = logging.getLogger()
 class DistributedJobManager:
     _default_instance: Optional['DistributedJobManager'] = None
 
+    @classmethod
+    def _sync_class(cls) -> None:
+        if cls._default_instance is not None:
+            pass  # no class-level attributes to sync
+
     def __init__(self) -> None:
         self.background_worker: Optional[threading.Thread] = None