Add ObjectBox as a write-behind persistence layer for Nostr events.
Events flowing through the relay pipeline are asynchronously batched
and written to ObjectBox on Dispatchers.IO. The LRU cache remains the
hot read path — no startup seeding or feed changes in this PR.
What's persisted: user's own events (all kinds), notes (kind 1),
profiles (kind 0), reposts (kind 6), reactions (kind 7), and zap
receipts (kind 9735).
Search now merges LRU cache results with ObjectBox for cross-session
note search. Old events are pruned on startup (50k cap, 90-day TTL,
user's own events exempt).
fiatjaf
Barry Deen