feat(ffi-iterator): Implementation of Iterator in Rust (1/4)

[AminR443]

This PR is a step towards implementing the FFI iterator mentioned in #1009.

This implement FFI functions (fwd_iter_on_root, fwd_iter_on_proposal, fwd_iter_next) in Rust, and also necessary changes in firewood crate for MerkleKeyValueStream to work with Arc<NodeStore<..>> as well.

[rkuris]

This is still a little confusing. The documentation is for this variant, but shouldn't the caller generally call fwd_free_owned_bytes regardless of which variant of KeyValueResult is returned, or must they check that it is this variant and only call that method if so?

[demosdemon]

idk your level of git foo, but here's how I normally resolve the gnarly merge conflicts from the squash and merge:

• Find the commit from the base branch where I merged main before the squash and merge,
• merge that specific commit into my child branch; this should be a clean merge unless there were conflicts between base branch and child branch
• merge the specific squash commit in main with the ours strategy; this should be a net-zero change (no tree updates)
• merge the rest of main

So, to resolve your conflicts with main now that my PR is merged, do:

# let git fetch the expired branch PR refs
git config --add remote.origin.fetch '+refs/pull/*/head:refs/remotes/origin/pr/*'
# fetch everything again
git fetch origin
git merge fcc07b8ba5e0716e3d8892a275010e77daaebbe5
git merge -s ours 8df1ccc1464f58839c732b57c6cd703e88137abc
git merge origin/main

The git config change will bloat your local repo. You can keep it if you want, but I do recommend removing it after, fetching again, and then running git prune and git gc to remove the bloat.

[rkuris]

This doc looks correct to me, but the comment is not resolved. Is there more to do here? If not, please mark this resolved.