Parse kill/item objectives from SMSG_QUEST_QUERY_RESPONSE binary data:
- extractQuestQueryObjectives() scans past the fixed integer header and
variable-length strings to reach the 4 entity + 6 item objective entries
(using known offsets: 40 fields for Classic/TBC, 55 for WotLK)
- Objectives stored in QuestLogEntry.killObjectives / itemObjectives arrays
- After storing, applyPackedKillCountsFromFields() reads 6-bit packed counts
from update-field slots (stride+2 / stride+3) and populates killCounts
using the parsed creature/GO entry IDs as keys
This means on login, quests that were in progress show correct kill count
progress (e.g. "2/5 Defias Bandits killed") without waiting for the first
server SMSG_QUESTUPDATE_ADD_KILL notification.