fix: Resolve F821 error and duplicate timestamp; enhance KB logging

This commit addresses two new issues introduced in recent changes:
- Corrected an F821 'Undefined name os' error in  by adding the missing import.
- Fixed a  in  which was a result of an incorrect merge during rebase.

Additionally, this commit finalizes the implementation of the 'Knowledge Base'
logging format in  by ensuring that
for  operations is correctly fetched from the graph store. This
guarantees that the new log format fully adheres to the design specifications,
providing complete and accurate information for update events.

Author: [email protected]

src/memos/mem_scheduler/general_scheduler.py

@@ -1,6 +1,7 @@
 import concurrent.futures
 import contextlib
 import json
+import os
 import traceback
 
 from memos.configs.mem_scheduler import GeneralSchedulerConfig
@@ -19,7 +20,6 @@
     PREF_ADD_LABEL,
     QUERY_LABEL,
     USER_INPUT_TYPE,
-    WORKING_MEMORY_TYPE,
 )
 from memos.mem_scheduler.schemas.message_schemas import ScheduleMessageItem
 from memos.mem_scheduler.schemas.monitor_schemas import QueryMonitorItem