chore: `task` and `message` package

internal/cache/cache.go

@@ -1 +0,0 @@
-package cache

internal/message/message.go

@@ -0,0 +1 @@
+package message

internal/task/task.go

@@ -1 +1,12 @@
+// manage task, such as file upload, file copy between accounts, offline download, etc.
 package task
+
+import "context"
+
+type Task struct {
+	Name     string
+	Func     func(context.Context) error
+	Status   string
+	Error    error
+	Progress int
+}