User book API: use a single query with result and count

internal/dto/out.go

@@ -16,6 +16,11 @@ type BookGet struct {
 }
 
 type BookUserGet struct {
+	Count int64             `json:"count"`
+	Books []BookUserGetBook `json:"books"`
+}
+
+type BookUserGetBook struct {
 	ID        uint   `json:"id"`
 	Title     string `json:"title" binding:"required,max=300"`
 	Author    string `json:"author" binding:"max=100"`