refactor(channelserver): extract QuestCache from Server struct

The quest cache fields (lock, data map, expiry map) were spread across
Server with manual lock management. The old read path also missed the
RLock entirely, creating a data race. Encapsulating in a dedicated type
fixes the race and reduces Server's field count by 2.

server/channelserver/quest_cache.go

@@ -0,0 +1,49 @@
+package channelserver
+
+import (
+	"sync"
+	"time"
+)
+
+// QuestCache is a thread-safe, expiring cache for parsed quest file data.
+type QuestCache struct {
+	mu     sync.RWMutex
+	data   map[int][]byte
+	expiry map[int]time.Time
+	ttl    time.Duration
+}
+
+// NewQuestCache creates a QuestCache with the given TTL in seconds.
+// A TTL of 0 disables caching (Get always misses).
+func NewQuestCache(ttlSeconds int) *QuestCache {
+	return &QuestCache{
+		data:   make(map[int][]byte),
+		expiry: make(map[int]time.Time),
+		ttl:    time.Duration(ttlSeconds) * time.Second,
+	}
+}
+
+// Get returns cached quest data if it exists and has not expired.
+func (c *QuestCache) Get(questID int) ([]byte, bool) {
+	if c.ttl <= 0 {
+		return nil, false
+	}
+	c.mu.RLock()
+	defer c.mu.RUnlock()
+	b, ok := c.data[questID]
+	if !ok {
+		return nil, false
+	}
+	if time.Now().After(c.expiry[questID]) {
+		return nil, false
+	}
+	return b, true
+}
+
+// Put stores quest data in the cache with the configured TTL.
+func (c *QuestCache) Put(questID int, b []byte) {
+	c.mu.Lock()
+	c.data[questID] = b
+	c.expiry[questID] = time.Now().Add(c.ttl)
+	c.mu.Unlock()
+}