feat: Use IMAP APPEND command to upload sync messages (#5845)

Why:
- With IMAP APPEND we can upload messages directly to the DeltaChat folder (for non-chatmail
  accounts).
- We can set the `\Seen` flag immediately so that if the user has other MUA, it doesn't alert about
  a new message if it's just a sync message (there were several such reports on the support
  forum). Though this also isn't useful for chatmail.
- We don't need SMTP envelope and overall remove some overhead on processing sync messages.

src/sync.rs

@@ -120,7 +120,7 @@ impl Context {
     /// Adds most recent qr-code tokens for the given group or self-contact to the list of items to
     /// be synced. If device synchronization is disabled,
     /// no tokens exist or the chat is unpromoted, the function does nothing.
-    /// The caller should perform `SchedulerState::interrupt_smtp()` on its own to trigger sending.
+    /// The caller should call `SchedulerState::interrupt_inbox()` on its own to trigger sending.
     pub(crate) async fn sync_qr_code_tokens(&self, grpid: Option<&str>) -> Result<()> {
         if !self.should_send_sync_msgs().await? {
             return Ok(());
@@ -153,7 +153,7 @@ impl Context {
             grpid: None,
         }))
         .await?;
-        self.scheduler.interrupt_smtp().await;
+        self.scheduler.interrupt_inbox().await;
         Ok(())
     }
 
@@ -233,17 +233,6 @@ impl Context {
             .body(json)
     }
 
-    /// Deletes IDs as returned by `build_sync_json()`.
-    pub(crate) async fn delete_sync_ids(&self, ids: String) -> Result<()> {
-        self.sql
-            .execute(
-                &format!("DELETE FROM multi_device_sync WHERE id IN ({ids});"),
-                (),
-            )
-            .await?;
-        Ok(())
-    }
-
     /// Takes a JSON string created by `build_sync_json()`
     /// and construct `SyncItems` from it.
     pub(crate) fn parse_sync_items(&self, serialized: String) -> Result<SyncItems> {
@@ -384,7 +373,12 @@ mod tests {
         );
 
         assert!(t.build_sync_json().await?.is_some());
-        t.delete_sync_ids(ids).await?;
+        t.sql
+            .execute(
+                &format!("DELETE FROM multi_device_sync WHERE id IN ({ids})"),
+                (),
+            )
+            .await?;
         assert!(t.build_sync_json().await?.is_none());
 
         let sync_items = t.parse_sync_items(serialized)?;
@@ -565,7 +559,7 @@ mod tests {
 
         // let alice's other device receive and execute the sync message,
         // also here, self-talk should stay hidden
-        let sent_msg = alice.pop_sent_msg().await;
+        let sent_msg = alice.pop_sent_sync_msg().await;
         let alice2 = TestContext::new_alice().await;
         alice2.set_config_bool(Config::SyncMsgs, true).await?;
         alice2.recv_msg_trash(&sent_msg).await;
@@ -593,7 +587,7 @@ mod tests {
             .set_config(Config::Displayname, Some("Alice Human"))
             .await?;
         alice.send_sync_msg().await?;
-        alice.pop_sent_msg().await;
+        alice.pop_sent_sync_msg().await;
         let msg = bob.recv_msg(&alice.pop_sent_msg().await).await;
         assert_eq!(msg.text, "hi");
 
@@ -628,7 +622,7 @@ mod tests {
         // group is promoted for compatibility (because the group could be created by older Core).
         // TODO: assert!(msg_id.is_none());
         assert!(msg_id.is_some());
-        let sent = alice.pop_sent_msg().await;
+        let sent = alice.pop_sent_sync_msg().await;
         let msg = alice.parse_msg(&sent).await;
         let mut sync_items = msg.sync_items.unwrap().items;
         assert_eq!(sync_items.len(), 1);