transaction: issue "new obsmarkers" message at the end of the transaction Instead of making bundle2 code responsible for this, it seems better to have it handled and the transaction level. First, it means the message will be more consistently printed. Second it means we won't spam the message over and over if the data arrive in multiple piece. Third, we are planning to move other similar message at the same level (for the same reason) so having them all at the same location will help us to control the order they are displayed.

debugobsolete: also issue the "new obsmarkers" messsage We are going to improve the way this message is issued in the core codebase. This will make it appears for `hg debugobsolete` too. Since this seems like a good idea, we make the output change in a previous changesets to clarify the next changeset.

split: use literal syntax to build a set of one element

rust-cpython: leverage py_shared_iterator::from_inner() where appropriate

rust-cpython: remove Option<_> from interface of py_shared_iterator It's the implementation detail of the py_shared_iterator that the leaked reference is kept in Option<_> so that it can be dropped early.

rust-cpython: rename py_shared_iterator_impl to py_shared_iterator It's a public interface now.

rust-cpython: replace dyn Iterator<..> of mapping with concrete type See the previous commit for why. The docstring is moved accordingly.

rust-cpython: replace dyn Iterator<..> of sequence with concrete type We wouldn't care the cost of the dynamic dispatch, but I feel a concrete type helps understanding error messages.

rust-dirstate: provide CopyMapIter and StateMapIter types They will be used in the declaration of Python iterator types.

rust-dirstate: specify concrete return type of DirsMultiset::iter() This allows us to put a returned iterator in a struct. We could implement DirsMultisetIter(hash_map::Keys<..>) struct to hide the implementation detail, but I think type alias is good enough for us.