feat(sync): implement pagination for historic_sync REQ+EOSE flow

Add automatic pagination support for non-Negentropy historic sync to handle
large result sets efficiently. When a subscription receives >= 75 events,
the system automatically fetches the next page using the 'until' parameter.

Changes:
- Add PaginationState struct to track event counts and min timestamps
- Add pagination_state HashMap to PendingBatch for per-subscription tracking
- Add PAGINATION_THRESHOLD constant (75 events)
- Pass pending_sync_index to event processor for state updates
- Track events and timestamps as they arrive
- Check threshold on EOSE and launch follow-up subscriptions
- Initialize pagination state when creating historic sync subscriptions
- Update test fixtures in algorithms.rs

The pagination continues recursively until a page returns fewer than 75 events,
ensuring complete historic data retrieval without overwhelming relay limits.

0 files changed, 0 insertions, 0 deletions