chore: whitelist 'ex' kwarg in _RedisLike Protocol

vulture flagged `ex` as 100% unused in `agentscore_commerce/stripe_multichain/pi_cache.py:45`. It's a kwarg name in the structural-typing Protocol matching `redis.asyncio.Redis.set(..., ex=)` — required for type-checking calls against the redis client, can't be removed.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: vvillait88

vulture_whitelist.py

@@ -5,6 +5,9 @@
 receive  # noqa: F821
 send  # noqa: F821
 
+# Redis SET kwarg in _RedisLike Protocol (structural type for redis.asyncio.Redis)
+ex  # noqa: F821
+
 # Public API exports
 Activity  # noqa: F821
 AgentScoreGate  # noqa: F821