Other(refactor): Sort safe.Mutex types before locking to prevent deadlocks

This change implements safe.Mutex and safe.RWMutex, which wrap the
sync.Mutex and sync.RWMutex types and are assigned a globally unique
integer ID. The safe.Lock and safe.RLock methods sort the mutexes
by this integer ID before locking to ensure that locks for a given
set of mutexes are always performed in the same order, avoiding
deadlocks.

internal/user/sync.go

@@ -110,7 +110,7 @@ func (user *User) sync(ctx context.Context) error {
 
 			return nil
 		})
-	}, &user.apiUserLock, &user.apiAddrsLock, &user.updateChLock)
+	}, user.apiUserLock, user.apiAddrsLock, user.updateChLock)
 }
 
 func syncLabels(ctx context.Context, client *liteapi.Client, updateCh ...*queue.QueuedChannel[imap.Update]) error {