chore: fix lint issues from performance optimization

- errcheck: check type assertions from sync.Pool.Get() in
  loadbalance/balancer.go and matcher/radix.go
- errcheck: check type assertion from list.Element.Value in
  resolver/resolver.go evictLRULocked
- revive: add doc comment for exported ReleaseMatchResult function

internal/loadbalance/balancer.go

@@ -41,7 +41,8 @@ var filterContextPool = sync.Pool{
 }
 
 func acquireFilterContext() *filterContext {
-	return filterContextPool.Get().(*filterContext)
+	fc, _ := filterContextPool.Get().(*filterContext)
+	return fc
 }
 
 func releaseFilterContext(fc *filterContext) {
@@ -633,5 +634,3 @@ func (t *Target) LastResolved() time.Time {
 	}
 	return time.Unix(0, nano)
 }
-
-

internal/matcher/radix.go

@@ -229,7 +229,7 @@ func (t *RadixTree) FindLongestPrefix(path string) *MatchResult {
 	if bestNode == nil {
 		return nil
 	}
-	result := matchResultPool.Get().(*MatchResult)
+	result, _ := matchResultPool.Get().(*MatchResult)
 	result.Handler = bestNode.handler
 	result.Path = bestNode.prefix
 	result.Priority = bestNode.priority
@@ -271,6 +271,7 @@ func (t *RadixTree) searchLongest(node *RadixNode, path string, bestNode *RadixN
 	return bestNode
 }
 
+// ReleaseMatchResult 将 MatchResult 归还到对象池。
 func ReleaseMatchResult(r *MatchResult) {
 	if r == nil {
 		return

internal/resolver/resolver.go

@@ -83,7 +83,7 @@ func (r *DNSResolver) evictLRULocked() {
 	if oldest == nil {
 		return
 	}
-	host := oldest.Value.(string)
+	host, _ := oldest.Value.(string)
 	delete(r.cache, host)
 	delete(r.lruIndex, host)
 	r.lruList.Remove(oldest)