docs(sports): state what ESPN_CHUNK_WORKERS was measured to do, not more

The comment claimed the sequential fetch made scoreboards blow the 20s
startup update() timeout. A boot on this branch still deferred 12 plugins
and timed out baseball-scoreboard while its season fetches took 0.74s and
1.12s: the startup budget is spent on other per-plugin work. Say what was
measured -- 17.7s sequential, 2.6-3.3s concurrent -- and nothing else.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/common/espn_dates.py

@@ -46,10 +46,9 @@ ESPN_MAX_LIMIT = 500
 # How long a rejected range keeps later ranges from being tried as ranges.
 RANGE_RETRY_SECONDS = 6 * 60 * 60
 
-# How many chunk requests may be in flight at once. A cold college-baseball
-# season is ~130 chunks once the busy months are re-asked day by day; asking
-# for them one at a time took long enough that scoreboard plugins blew the
-# 20s update() timeout on first run. Kept under requests' default
+# How many chunk requests may be in flight at once. Four busy months of
+# college baseball are ~130 chunks once each is re-asked day by day: 17.7s one
+# at a time on a Pi 4, 2.6-3.3s six at a time. Kept under requests' default
 # pool_maxsize of 10 so the shared Session never has to discard connections.
 ESPN_CHUNK_WORKERS = 6
 
@@ -272,9 +271,10 @@ def fetch_espn_date_chunks(
 
     # A month that came back at the cap is truncated; its days replace it in
     # place, so merged events stay in chunk order however the requests raced.
-    slots: List[Any] = list(results)
+    slots: List[Any] = results
     capped: Dict[int, List[str]] = {}
-    for index, (chunk, payload) in enumerate(zip(chunks, results)):
+    for index, chunk in enumerate(chunks):
+        payload = slots[index]
         if payload is None or len(chunk) != 6:
             continue
         events = payload.get("events") if isinstance(payload, dict) else None
@@ -285,6 +285,13 @@ def fetch_espn_date_chunks(
                     chunk, ESPN_MAX_LIMIT,
                 )
             capped[index] = _days_of_month(chunk)
+            # Drop the truncated month now rather than after its days arrive:
+            # a capped college-baseball month is ~2MB of parsed JSON, and
+            # holding four of them through ~120 day requests added ~25MB to
+            # the peak -- more than the concurrency itself. Low-memory boards
+            # (docs/LOW_MEMORY_BOARDS.md) have under 200MB of headroom.
+            slots[index] = None
+    payload = events = None
 
     if capped:
         days = [day for index in sorted(capped) for day in capped[index]]