初步实验使用KV数据库（pebble）存储缓存索引

internal/utils/kvstore/errors.go

@@ -0,0 +1,18 @@
+// Copyright 2024 GoEdge CDN goedge.cdn@gmail.com. All rights reserved. Official site: https://goedge.cn .
+
+package kvstore
+
+import (
+	"errors"
+	"github.com/cockroachdb/pebble"
+)
+
+var ErrTableNotFound = errors.New("table not found")
+var ErrKeyTooLong = errors.New("too long key")
+
+func IsKeyNotFound(err error) bool {
+	if err == nil {
+		return false
+	}
+	return errors.Is(err, pebble.ErrNotFound)
+}