## Issue Addressed
#4127. PR to test port conflicts in CI tests .
## Proposed Changes
See issue for more details, potential solution could be adding a cache bound by time to the `unused_port` function.
## 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>
