refactor: rename _ex() -> _ext()

"ex" means "used to be, but no longer is".
"ext" means "extended", which is the intended meaning.
"Ext" is more common not only in the Rust ecosystem but in general.
We already had several people (myself included) asking
what "ex" is supposed to mean.

To reproduce this commit, search and replace `_ex(?!\w)` -> `_ext`.
But don't change `list_transports_ex` because it's public API.

src/tests/pre_messages/forward_and_save.rs

@@ -107,7 +107,7 @@ async fn test_receive_both() -> Result<()> {
     forward_msgs(alice, &[alice_msg_id], alice_chat_id).await?;
     let rev_order = false;
     let msg = bob
-        .recv_msg(&alice.pop_sent_msg_ex(rev_order).await.unwrap())
+        .recv_msg(&alice.pop_sent_msg_ext(rev_order).await.unwrap())
         .await;
     assert_eq!(msg.download_state(), DownloadState::Available);
     assert_eq!(msg.is_forwarded(), true);

src/tests/pre_messages/receiving.rs

@@ -318,7 +318,7 @@ async fn pre_msg_mdn_before_sending_full(text: &str) -> Result<()> {
     msg.set_text(text.to_string());
     chat::send_msg(alice, alice_chat_id, &mut msg).await?;
     let rev_order = false;
-    let pre_msg = alice.pop_sent_msg_ex(rev_order).await.unwrap();
+    let pre_msg = alice.pop_sent_msg_ext(rev_order).await.unwrap();
     let alice_msg_id = msg.id;
 
     let msg = bob.recv_msg(&pre_msg).await;