revert(vegas): gate only the prefetch thread; gating ESPN fetches measured worse

84043468 also gated the ESPN chunk fetches and the background data
service's workers, for the hourly sports refresh. A burst test on hdpi
(baseball and football refreshing every 5 minutes, 10-minute soaks, G F F G):

  G  prefetch gated only        0.87%, 0.83% late; 6+ late 20, 16; fetches 0.3-1.8s
  F  + fetch threads gated      1.23%, 1.05% late; 6+ late 12, 16; fetches 1.6-4.6s

Every parked fetch thread wakes at each swap and has to take the GIL again
just to park at the end of the window, so twenty of them cost more than
they saved, and the fetches ran two to three times as long. The plugins'
own copies of espn_dates (half the burst) were never gated anyway.

espn_dates and the background data service go back to main's versions and
the module-level active gate goes. Kept from that commit: the render thread
is never gated, a live refresh from another thread can't take its place,
and nested blocks keep the outer boundary.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/background_data_service.py

@@ -26,7 +26,6 @@ from enum import Enum
 from concurrent.futures import ThreadPoolExecutor
 import pytz
 from src.cache_manager import CacheManager
-from src.common import render_gate
 from src.common.json_body import response_json
 from src.common.espn_dates import (
     RANGE_RETRY_SECONDS,
@@ -318,12 +317,6 @@ class BackgroundDataService:
         return request_id
     
     def _fetch_data_worker(self, request: FetchRequest) -> FetchResult:
-        """Fetch one request on a worker thread, giving way to Vegas's render
-        thread while it scrolls (src/common/render_gate.py)."""
-        with render_gate.yielding():
-            return self._fetch_data(request)
-
-    def _fetch_data(self, request: FetchRequest) -> FetchResult:
         """
         Worker function that performs the actual data fetching.