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/misc.py

@@ -1193,7 +1193,7 @@ def stream_chunks_handler(stream: aiohttp.StreamReader):
                     if len(line) > max_buffer_size:
                         skip_mode = True
                         yield b'data: {}\n'
-                        log.info(f'Skip mode triggered, line size: {len(line)}')
+                        log.info('Skip mode triggered, line size: %s', len(line))
                     else:
                         yield line + b'\n'
 
@@ -1203,7 +1203,7 @@ def stream_chunks_handler(stream: aiohttp.StreamReader):
             # Check if buffer exceeds limit
             if not skip_mode and len(buffer) > max_buffer_size:
                 skip_mode = True
-                log.info(f'Skip mode triggered, buffer size: {len(buffer)}')
+                log.info('Skip mode triggered, buffer size: %s', len(buffer))
                 # Clear oversized buffer to prevent unlimited growth
                 buffer = b''