Add Infinite Chat History tutorial

[lyndonbauto]

Summary

• docs/tutorials/infinite-chat-history.md — Aerospike docs tutorial for long agent conversations on adk-aerospike >=0.1.0 segment storage
• 20,000-turn synthetic demo: append-only segments, full hydrate vs num_recent_events / after_timestamp
• Documents read latency: recent-X is ~1–50 ms (X=5–500); full 20k hydrate ~2.8 s on Docker CE

Test plan

• 20,000 sequential append_event — 27 segments, full get_session returns 20,000 events
• num_recent_events / after_timestamp spot checks
• list_sessions returns session row only (no segment leak)