Refa: asyncio.to_thread to ThreadPoolExecutor to break thread limitat… (#12716)

### Type of change

- [x] Refactoring

deepdoc/vision/t_ocr.py

@@ -18,6 +18,10 @@ import asyncio
 import logging
 import os
 import sys
+
+
+from common.misc_utils import thread_pool_exec
+
 sys.path.insert(
     0,
     os.path.abspath(
@@ -64,9 +68,9 @@ def main(args):
         if limiter:
             async with limiter:
                 print(f"Task {i} use device {id}")
-                await asyncio.to_thread(__ocr, i, id, img)
+                await thread_pool_exec(__ocr, i, id, img)
         else:
-            await asyncio.to_thread(__ocr, i, id, img)
+            await thread_pool_exec(__ocr, i, id, img)
 
 
     async def __ocr_launcher():