♻️ refactor(delete): use GmailClient for message list creation

- use GmailClient struct for creating a new message list
- this change improve code maintainability and testability

src/delete.rs

@@ -1,6 +1,6 @@
 use google_gmail1::api::BatchDeleteMessagesRequest;
 
-use crate::{MessageList, Result};
+use crate::{GmailClient, MessageList, Result};
 
 /// Struct for deleting messages
 #[derive(Debug)]
@@ -10,8 +10,8 @@ pub struct Delete {
 
 impl Delete {
     /// Create a new Delete struct
-    pub async fn new(credential: &str) -> Result<Self> {
-        let message_list = MessageList::new(credential).await?;
+    pub async fn new(client: &GmailClient) -> Result<Self> {
+        let message_list = MessageList::new(client).await?;
         Ok(Delete { message_list })
     }