chore: update memo service (#1138)

* chore: update memo service

* chore: update

api/memo.go

@@ -1,5 +1,8 @@
 package api
 
+// MaxContentLength means the max memo content bytes is 1MB.
+const MaxContentLength = 1 << 30
+
 // Visibility is the type of a visibility.
 type Visibility string
 
@@ -37,7 +40,6 @@ type Memo struct {
 	Content    string     `json:"content"`
 	Visibility Visibility `json:"visibility"`
 	Pinned     bool       `json:"pinned"`
-	DisplayTs  int64      `json:"displayTs"`
 
 	// Related fields
 	Creator      *User       `json:"creator"`
@@ -86,8 +88,8 @@ type MemoFind struct {
 	VisibilityList []Visibility
 
 	// Pagination
-	Limit  int
-	Offset int
+	Limit  *int
+	Offset *int
 }
 
 type MemoDelete struct {