perf: use the orjson codec to parse Jupyter kernel messages (#27812)

The code interpreter parses every message from the Jupyter kernel websocket with stdlib `json`, in a loop that runs for the duration of an execution. Messages carrying large stdout or a base64 image payload are the expensive ones.

It now goes through `JSONCodec`, which selects orjson when `ENABLE_ORJSON` is set. Every consumer of the parsed message reads strings only: `content.text`, `content.data['text/plain']` and `['image/png']`, `content.traceback`, and `content.execution_state`. Jupyter renders large integers into `text/plain` as strings rather than JSON numbers, so no numeric round trip is involved.

The one-shot `execute_request` message this module sends keeps stdlib `json`; it is a small fixed-shape dict sent once per execution.

With `ENABLE_ORJSON` unset, which is the default, `JSONCodec` is stdlib `json` and this call site behaves exactly as before.

backend/open_webui/utils/code_interpreter.py

@@ -7,6 +7,7 @@ from typing import Optional
 import aiohttp
 import websockets
 from open_webui.env import AIOHTTP_CLIENT_ALLOW_REDIRECTS
+from open_webui.utils.json_codec import JSONCodec
 from pydantic import BaseModel
 
 logger = logging.getLogger(__name__)
@@ -157,7 +158,7 @@ class JupyterCodeExecuter:
             try:
                 # wait for message
                 message = await asyncio.wait_for(ws.recv(), self.timeout)
-                message_data = json.loads(message)
+                message_data = JSONCodec.loads(message)
                 # msg id not match, skip
                 if message_data.get('parent_header', {}).get('msg_id') != msg_id:
                     continue