fix: silence ty 0.0.87 override checks on narrowed faststream attributes

[lesnik512]

Fixes #209.

The scheduled dependency check picked up ty 0.0.87, which turns on invalid-mutable-override by default and now checks overrides of attributes declared in __init__. It reports six errors on main.

Each one is a subclass narrowing an attribute it inherits from faststream: _outer_config: OutboxBrokerConfig four times, broker: _OutboxBroker on the FastAPI router, and _subscribers: WeakSet[OutboxSubscriber] on the broker. faststream's bases aren't generic over these types, so we can't express the narrowing soundly. Each line gets a # ty: ignore[...] for its rule. Nothing changes at runtime.

Locally with ty 0.0.87, just lint-ci is clean and the full suite passes against Postgres 17 (626 passed, 100% coverage).

[github-actions]

Benchmark gate

✅ gate passed

scenario	msg/s	delete/msg	WALrec/msg	WALB/msg	fpi	upd	del	dead_tup
consumer/w1/b10	1369	1.000	6.80	912	242	5000	5000	10000
consumer/w1/b100	1395	1.000	6.86	917	243	5000	5000	10000
consumer/w2/b10	1740	1.000	6.78	954	242	5000	5000	10000
consumer/w2/b100	2164	1.000	6.73	955	243	5000	5000	10000
consumer/w4/b10	1637	1.000	6.68	921	242	5000	5000	10000
consumer/w4/b100	2517	1.000	6.86	1035	243	5000	5000	10000
consumer/w1/b100/tfbs100	9708	0.010	6.07	1116	243	5000	5000	10000
producer/w1/b100	4444	0.000	3.04	584	0	0	0	0

Gated (fails the build): delete_calls + tuple counters (upd/del/ins) + the producer's insert_calls, exact; select_calls within +2; wal_records within a 10% band. msg/s, WAL bytes and total calls are informational (timing/FPI noise).