fix: switch to aiofiles for asynchronous file reading in viz2d_job_file

app.py

@@ -1,3 +1,4 @@
+import aiofiles
 import asyncio
 import base64
 import io
@@ -1146,9 +1147,9 @@ async def viz2d_job_file(job_id: str):
     bundle_path = JOB_DIR / f"{job_id}.bundle.json"
     if not bundle_path.exists():
         raise HTTPException(status_code=404, detail="Job output not found.")
-    def iter_file():
-        with open(bundle_path, "rb") as f:
-            while chunk := f.read(65536):
+    async def iter_file():
+        async with aiofiles.open(bundle_path, "rb") as f:
+            while chunk := await f.read(65536):
                 yield chunk
 
     return StreamingResponse(iter_file(), media_type="application/json")