[Performance] Reworked how client to NPC aggro checks are made

- Before when reverse aggro checks were done (client to NPC), checks would happen every 750 millseconds where a client would
		check an entire entity list with distance calcs and other checks for aggro, with many clients in a zone and many NPC's this would
		add a lot of unecessary overhead. A temporary adjustment on 3/25 was made and upped the check to 6 seconds.
	- Now, there is a new methodology to scanning. The client will build a cache list of NPC's within close range as defined in new rule:
		RULE_INT(Range, ClientNPCScan, 300) and will also get any NPC that has an aggro range beyond that defined range to use in
		the frequent checks for aggro, the result is far less overhead
	- Client scanning changes when moving versus not moving, the client will scan aggro every 500 milliseconds while moving, and
		3000 millseconds aggro check when not moving, with a 6000ms re-fetch for close NPC's
	- A demo of these changes can be found here:
		https://youtu.be/aGroiwLSTVU

zone/client.cpp

@@ -135,7 +135,7 @@ Client::Client(EQStreamInterface* ieqs)
 	forget_timer(0),
 	autosave_timer(RuleI(Character, AutosaveIntervalS) * 1000),
 #ifdef REVERSE_AGGRO
-	scanarea_timer(RuleI(Aggro, ClientAggroCheckInterval) * 1000),
+	client_scan_npc_aggro_timer(RuleI(Aggro, ClientAggroCheckInterval) * 1000),
 #endif
 	tribute_timer(Tribute_duration),
 	proximity_timer(ClientProximity_interval),
@@ -160,7 +160,8 @@ Client::Client(EQStreamInterface* ieqs)
 	m_AutoAttackPosition(0.0f, 0.0f, 0.0f, 0.0f),
 	m_AutoAttackTargetLocation(0.0f, 0.0f, 0.0f),
 	last_region_type(RegionTypeUnsupported),
-	m_dirtyautohaters(false)
+	m_dirtyautohaters(false),
+	npc_close_scan_timer(6000)
 {
 	for(int cf=0; cf < _FilterCount; cf++)
 		ClientFilters[cf] = FilterShow;
@@ -358,6 +359,8 @@ Client::~Client() {
 		m_tradeskill_object = nullptr;
 	}
 
+	close_npcs.clear();
+
 	if(IsDueling() && GetDuelTarget() != 0) {
 		Entity* entity = entity_list.GetID(GetDuelTarget());
 		if(entity != nullptr && entity->IsClient()) {