reconstruct state data

If the state file is missing, we can reconstruct which parts were
exported based on revision ids

Also, packages could have branches in Git, but not be in Git. We
need to check (project,package) tuple for this and not just abort
based on the package name alone.

lib/flat_walker.py

@@ -20,7 +20,7 @@ class FlatTreeWalker(AbstractWalker):
 
     def __init__(self, rebase_devel=False) -> None:
         super().__init__()
-        self.flats = []
+        self.flats:list[FlatNode] = []
         # the rebase_devel won't work as such as rebasing the branch needs an explicit action
         self.rebase_devel = rebase_devel
         # remember the last merge point so we can know the parent of it for the root of the sources