初步实现bfs原型（仅用于实验）

internal/utils/bfs/errors.go

@@ -0,0 +1,13 @@
+// Copyright 2024 GoEdge CDN goedge.cdn@gmail.com. All rights reserved. Official site: https://goedge.cn .
+
+package bfs
+
+import "errors"
+
+var ErrClosed = errors.New("the file closed")
+var ErrInvalidHash = errors.New("invalid hash")
+var ErrFileIsWriting = errors.New("the file is writing")
+
+func IsWritingErr(err error) bool {
+	return err != nil && errors.Is(err, ErrFileIsWriting)
+}