performance: optimize packet broadcasting by caching entity snapshots

- Add snapshot caching for entity stats, vitals, statuses and player equipment
- Cache per-(player,npc) aggression to skip unchanged NpcAggressionPacket sends
- Cache per-(player,map) visible map-items hash to avoid regenerating identical MapItemsPacket data
- Skip redundant broadcasts when cached state matches current values
- Clear all snapshots when entities leave map/layer/instance (including player/npc aggression)
- Batch vital and status updates to only include entities with actual changes
- Equipment broadcasts now only send when items change

These changes significantly reduce network bandwidth and server CPU in high-entity scenarios (raids, events, crowded maps) by eliminating unnecessary/duplicate packet transmissions to clients while preserving first-send guarantees and correctness. Behavior is fully backwards-compatible; clients see the same game state with less packet noise and lower latency impact from server-side broadcasting.

Author: Arufonsu