fix(catalog): a 24/7 stream archive's years-long length is unknown, not summed or sorted by

YouTube reports a 24/7 stream's archive with the years it has run (prod: 122,962,914 s), and one
such video made the Watch later total read 44,073 hours. A length past a day is now no length
(`Video.length_seconds`, LENGTH_MAX_S): the API sends none, the playlist and channel totals
leave it out and count it as `live_without_length` ("+N live" beside the sum), and the duration
filter, sort and Home budget never match it. Migration 0117 moves the duration sort indexes onto
the length expression. An AST test holds who may still read the raw column.

The migration 0110 test now ends its read before the way down: 0117 builds an index
CONCURRENTLY there, which waited for that open transaction forever.

backend/tests/test_migration_0110.py

@@ -45,6 +45,9 @@ def test_an_interval_override_moves_into_sysconfig_and_back(db):
         }
         assert conn.execute(text("SELECT to_regclass('scheduler_settings')")).scalar() is None
     assert scheduler.load_intervals(db)["rss_poll"] == 25
+    # The way down rebuilds an index CONCURRENTLY (0117), which waits for every open transaction —
+    # the read above left this session's open.
+    db.rollback()
 
     command.downgrade(cfg, "0109_job_runs")
     try: