performance: optimize entity packet broadcasting

[Arufonsu]

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.

[pandinocoder]

How does the cache interact with clients connecting after the cache is established? Does the cache get hit there and skip sending values to them?

Does the cache properly clear when NPCs and players die/spawn/connect/disconnect?

[Arufonsu]

How does the cache interact with clients connecting after the cache is established? Does the cache get hit there and skip sending values to them?

Does the cache properly clear when NPCs and players die/spawn/connect/disconnect?

When clients connect:

• SendMap → GenerateMapEntitiesPacket creates new EntityPacket objects for all visible entities
• SendEntityDataTo(player, entity) sends direct uncached packets to the specific connecting player
• The snapshot caching only affects proximity broadcasts (equipment, stats, vitals, aggression)
• New players always get the full initial state, then subsequent updates use caching

The cache is cleared via:

• Death: All entity types (Player, Npc, Resource) call SendEntityDie(entity) which includes ClearEntitySnapshotCache(en)
• Map transitions: SendEntityLeaveMap, SendEntityLeave, SendEntityLeaveLayer, SendEntityLeaveInstanceOfMap all clear the cache
• ClearNpcAggressionSnapshot: Both NPC death and player disconnect (entity leave) remove their aggression cache