fix: wait on loguru to flush async logs from services (#7908)

Allow loguru to flush async logs from services

src/backend/base/langflow/main.py

@@ -191,7 +191,10 @@ def get_lifespan(*, fix_migration=False, version=None):
                 sync_flows_from_fs_task.cancel()
                 await asyncio.wait([sync_flows_from_fs_task])
             await teardown_services()
+
+            await asyncio.sleep(0.1)  # let logger flush async logs
             await logger.complete()
+
             temp_dir_cleanups = [asyncio.to_thread(temp_dir.cleanup) for temp_dir in temp_dirs]
             await asyncio.gather(*temp_dir_cleanups)
             # Final message