Turn spr into a stacked Github collaboration library

[alper]

I looked around a bit and there a bunch of projects that patch alternate non-branch workflows into git. The problem is that most of them don't have anything to make working with Github easy.

See for instance:

• Integrate with Github pull requests arxanas/git-branchless#45
• Add support for pushing stacked reviews to GitHub, GitLab, etc. martinvonz/jj#485

spr covers the GitHub workflow part (in a much more straightforward way than any other project really) but doesn't go much further than that. Most of these tools also seem to be written in Rust. Could these two things be combined?

Not sure how much of an effort it would be but could spr be turned into a library for sending sequences of commits to Github and keeping them in sync?