Add method to check connection capabilities

Before, the check was being done on the capabilities set directly.

melib/src/backends/imap.rs

@@ -469,12 +469,9 @@ impl MailBackend for ImapType {
                 ImapProtocol::IMAP {
                     extension_use: ImapExtensionUse { idle, .. },
                 } => {
-                    idle && uid_store
-                        .capabilities
-                        .lock()
-                        .unwrap()
-                        .iter()
-                        .any(|cap| cap.eq_ignore_ascii_case(b"IDLE"))
+                    let main_conn_lck = timeout(uid_store.timeout, main_conn.lock()).await?;
+
+                    idle && main_conn_lck.has_capability("IDLE".to_string())
                 }
                 _ => false,
             };

melib/src/backends/imap/connection.rs

@@ -840,6 +840,14 @@ impl ImapConnection {
         }
     }
 
+    pub fn has_capability(&self, capability: String) -> bool {
+        self.capabilities
+            .lock()
+            .unwrap()
+            .iter()
+            .any(|cap| cap.eq_ignore_ascii_case(&capability.as_bytes()))
+    }
+
     pub async fn select_mailbox(
         &mut self,
         mailbox_hash: MailboxHash,