feat(common): sports_live_fetch -- the reconciled live fetch and odds (sports family 9) (#793)

New hardware-free module src/common/sports_live_fetch.py, copied from
ledmatrix-plugins claude/family9-reconcile once the nine scoreboards made
_fetch_todays_games (seven bodies when measured) and _fetch_odds (three) one
body each. Both live on the plugins' SportsCore, so one mixin,
SportsLiveFetchMixin, carries exactly those two plus the odds worker
_drain_odds_queue; no manager gains a method it lacks today.

Owner decisions (2026-10-12):
- Live scores are always fresh: every poll asks ESPN through
  get_espn_scoreboard and leaves the answer under the shared
  espn_scoreboard_cache_key for its dates (max_age=1: only a copy another
  reader fetched within the last second is reused). The plugins' 30 s
  <sport_key>_scoreboard_current cache is gone.
- College basketball is asked by date like every other league (ESPN
  answered single dates for both college leagues on 2026-10-12).
- Odds never block update(): one daemon worker per manager answers a queue
  and attaches each line in place under _games_lock; one batch in flight per
  manager, games queued meanwhile join it, every dict queued for an id gets
  the one answer. show_odds, the two odds intervals and a missing odds
  manager (debug, not ERROR) are respected.
- An answer whose events is not a list is no games.

Fix: get_espn_scoreboard() no longer caches an answer whose events is not a
list ("events": null), which every reader of the shared key inherited; it is
still returned to the caller.

- test/test_sports_live_fetch.py: the plugins' pinned cases (requests,
  dates and keys at 10:00 and 02:00 Eastern, freshness, malformed and failed
  answers, odds that never block and land later, the intervals, one batch per
  manager, a worker that cannot start, update and display on two threads),
  plus the host contract. Mutation-checked (11 mutants, all caught).
- test/test_sports_live_fetch_parity.py: with LEDMATRIX_PLUGINS, compares
  each body with every plugin copy. Passes against claude/family9-reconcile;
  fails against the pre-reconcile tree.
- test/test_espn_scoreboard_cache.py: the null-events regression.
- mypy ratchet, src/common/README.md, CHANGELOG (Unreleased: New modules,
  Fixes), docs/SPORTS_UNIFICATION.md family 9 status and decisions.

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

test/test_espn_scoreboard_cache.py

@@ -392,6 +392,15 @@ class TestGetEspnScoreboard:
                                 "20261004", cache_manager=cache)
         assert cache.records == {}
 
+    @pytest.mark.parametrize("payload", [{"events": None}, {}, {"events": "x"}, []])
+    def test_an_answer_without_an_events_list_is_returned_not_cached(self, service, payload):
+        espn = Espn()
+        espn.get = lambda url, **kwargs: _response(payload, url, None)
+        cache = RecordCache()
+        assert get_espn_scoreboard(espn, "football", "nfl", "20261004",
+                                   cache_manager=cache) == payload
+        assert cache.records == {}
+
     def test_no_cache_manager_just_fetches(self, service):
         espn = Espn()
         get_espn_scoreboard(espn, "football", "nfl", "20261004")