This PR tinkers a bit with building a test helper to run integration
tests that are still ~lightweight against a real gitserver.
The caller can either clone a real repo to disk / embed it in the git
repo, or can create a small repo on the fly, and then get a running
gitserver gRPC server that returns all the data required.
These tests should only exist outside of cmd/ and internal/, as there is
a big potential to do cross-cmd imports from here, which can cause bad
coupling. But for just these tests, that should be fine.
The most trivial rockskip indexing job that I put in here to POC this
runs in 6.3s, including all setup and teardown. That seems very
reasonable to me.
Test plan:
The POC test passes.
