## Issue Addressed
NA
## Proposed Changes
This PR extends #3018 to address my review comments there and add automated integration tests with Geth (and other implementations, in the future).
I've also de-duplicated the "unused port" logic by creating an `common/unused_port` crate.
## Additional Info
I'm not sure if we want to merge this PR, or update #3018 and merge that. I don't mind, I'm primarily opening this PR to make sure CI works.
Co-authored-by: Mark Mackey <mark@sigmaprime.io>
