refactor(imap): remove Session from Imap structure

Connection establishment now happens only in one place in each IMAP loop.
Now all connection establishment happens in one place
and is limited by the ratelimit.

Backoff was removed from fake_idle
as it does not establish connections anymore.
If connection fails, fake_idle will return an error.
We then drop the connection and get back to the beginning of IMAP
loop.

Backoff may be still nice to have to delay retries
in case of constant connection failures
so we don't immediately hit ratelimit if the network is unusable
and returns immediate error on each connection attempt
(e.g. ICMP network unreachable error),
but adding backoff for connection failures is out of scope for this change.

src/context.rs

@@ -461,13 +461,13 @@ impl Context {
 
         // connection
         let mut connection = Imap::new_configured(self, channel::bounded(1).1).await?;
-        connection.prepare(self).await?;
+        let mut session = connection.prepare(self).await?;
 
         // fetch imap folders
         for folder_meaning in [FolderMeaning::Inbox, FolderMeaning::Mvbox] {
             let (_, watch_folder) = convert_folder_meaning(self, folder_meaning).await?;
             connection
-                .fetch_move_delete(self, &watch_folder, folder_meaning)
+                .fetch_move_delete(self, &mut session, &watch_folder, folder_meaning)
                 .await?;
         }
 
@@ -484,10 +484,8 @@ impl Context {
         };
 
         if quota_needs_update {
-            if let Some(session) = connection.session.as_mut() {
-                if let Err(err) = self.update_recent_quota(session).await {
-                    warn!(self, "Failed to update quota: {err:#}.");
-                }
+            if let Err(err) = self.update_recent_quota(&mut session).await {
+                warn!(self, "Failed to update quota: {err:#}.");
             }
         }