初步实验使用KV数据库（pebble）存储缓存索引

internal/utils/kvstore/iterator_options.go

@@ -0,0 +1,17 @@
+// Copyright 2024 GoEdge CDN goedge.cdn@gmail.com. All rights reserved. Official site: https://goedge.cn .
+
+package kvstore
+
+import "github.com/cockroachdb/pebble"
+
+type IteratorOptions struct {
+	LowerBound []byte
+	UpperBound []byte
+}
+
+func (this *IteratorOptions) RawOptions() *pebble.IterOptions {
+	return &pebble.IterOptions{
+		LowerBound: this.LowerBound,
+		UpperBound: this.UpperBound,
+	}
+}