fix: run Frigate+ API calls in thread pool to prevent event loop blocking

The send_to_plus and set_false_positive handlers are async but call
synchronous PlusApi methods (which use the requests library) directly,
blocking the asyncio event loop for 10-16 seconds during image upload.
This stalls all other HTTP requests to Frigate.

Wrap upload_image, add_annotation, and add_false_positive calls in
asyncio.to_thread() so they run in a thread pool without blocking.

Fixes #16566

frigate/api/event.py

@@ -1,5 +1,6 @@
 """Event apis."""
 
+import asyncio
 import base64
 import datetime
 import json
@@ -11,7 +12,6 @@ from functools import reduce
 from pathlib import Path
 from typing import List
 from urllib.parse import unquote
-import asyncio
 
 import cv2
 import numpy as np
@@ -1125,7 +1125,9 @@ async def send_to_plus(request: Request, event_id: str, body: SubmitPlusBody = N
         )
 
     try:
-        plus_id = await asyncio.to_thread(request.app.frigate_config.plus_api.upload_image, image, event.camera)
+        plus_id = await asyncio.to_thread(
+            request.app.frigate_config.plus_api.upload_image, image, event.camera
+        )
     except Exception as ex:
         logger.exception(ex)
         return JSONResponse(
@@ -1232,7 +1234,8 @@ async def false_positive(request: Request, event_id: str):
     )
 
     try:
-        request.app.frigate_config.plus_api.add_false_positive(
+        await asyncio.to_thread(
+            request.app.frigate_config.plus_api.add_false_positive,
             event.plus_id,
             region,
             box,