rust-index: handle `MixedIndex` in `pyindex_to_graph` On the long run we will want to implement the Graph trait directly in Rust, but for now we take the path with the least amount of change to focus on the coming persistent NodeMap code. We test this new code through with the lazy ancestors code. Differential Revision: https://phab.mercurial-scm.org/D7657

rust-index: make it possible to clone the struct referencing the C index If we are to hand over the C index object to other code, we need to be able to create a new python reference to it. Differential Revision: https://phab.mercurial-scm.org/D7656