fix: set connectivity state to working immediately after connecting

"Connected" state actually means that that connection is there,
but Delta Chat currently has no use for it.
`all_work_done()` retruns true for Connected state
and false for Working state.
We do not want all_work_done() to return true immediately
after calling start_io(), but only when connection goes idle.

src/imap.rs

@@ -404,7 +404,7 @@ impl Imap {
                     "IMAP-LOGIN as {}",
                     self.config.lp.user
                 )));
-                self.connectivity.set_connected(context).await;
+                self.connectivity.set_working(context).await;
                 info!(context, "Successfully logged into IMAP server");
                 Ok(())
             }

src/scheduler/connectivity.rs

@@ -33,8 +33,13 @@ enum DetailedConnectivity {
     #[default]
     Uninitialized,
     Connecting,
+
+    /// State set immediately after connecting.
+    /// This means connection is established, but connection is not idle yet.
     Working,
     InterruptingIdle,
+
+    /// Connection is established and is idle.
     Connected,
 
     /// The folder was configured not to be watched or configured_*_folder is not set