feat: parse and display item level and required level in tooltips

- Add itemLevel/requiredLevel fields to ItemQueryResponseData (parsed
  from SMSG_ITEM_QUERY_SINGLE_RESPONSE) and ItemDef
- Propagate through all 5 rebuildOnlineInventory() paths
- Show "Item Level N" and "Requires Level N" in item tooltip in
  standard WoW order (below item name, above required level/stats)

src/game/world_packets.cpp

@@ -2449,8 +2449,8 @@ bool ItemQueryResponseParser::parse(network::Packet& packet, ItemQueryResponseDa
 
     packet.readUInt32(); // AllowableClass
     packet.readUInt32(); // AllowableRace
-    packet.readUInt32(); // ItemLevel
-    packet.readUInt32(); // RequiredLevel
+    data.itemLevel = packet.readUInt32();
+    data.requiredLevel = packet.readUInt32();
     packet.readUInt32(); // RequiredSkill
     packet.readUInt32(); // RequiredSkillRank
     packet.readUInt32(); // RequiredSpell