perf: build info log messages lazily so raising the log level actually saves work (#27837)

Raising GLOBAL_LOG_LEVEL to WARNING buys quieter output but not less work: 241 INFO call sites interpolate their payload into an f-string before the logging call gets to drop it. The heaviest is get_doc, which logs every chunk id and metadata dict in a collection, so on the full-context retrieval path that is the entire knowledge base, once per chat request.

That one line at WARNING, CPython 3.12:

| knowledge base | payload | before   | after   |
| -------------- | ------- | -------- | ------- |
| top-k of 3     | 1.2 kB  | 3.8 us   | 0.07 us |
| 500 chunks     | 201 kB  | 583.6 us | 0.08 us |
| 5000 chunks    | 2.0 MB  | 5.8 ms   | 0.15 us |

The lazy form log.info('query_doc:result %s %s', result.ids, result.metadatas) hands the payload to record.getMessage(), which the InterceptHandler only reaches once a record has passed the level check. Output at INFO is byte-identical. Two sites that already built their message eagerly, one str concat and one % operator, move to the same lazy form.

backend/open_webui/utils/chat.py

@@ -68,7 +68,7 @@ async def generate_direct_chat_completion(
         )
 
     channel = f'{user_id}:{session_id}:{request_id}'
-    logging.info(f'WebSocket channel: {channel}')
+    logging.info('WebSocket channel: %s', channel)
 
     if form_data.get('stream'):
         q = asyncio.Queue()
@@ -95,7 +95,7 @@ async def generate_direct_chat_completion(
             }
         )
 
-        log.info(f'res: {res}')
+        log.info('res: %s', res)
 
         if res.get('status', False):
             # Define a generator to stream responses