chore: simplify interop test implementation

[achingbrain]

Aligns interop test implementation with https://github.com/libp2p/test-plans/pull/365

Change checklist

• [x] I have performed a self-review of my own code
• [ ] I have made corresponding changes to the documentation if necessary (this includes comments as well)
• [x] I have added tests that prove my fix is effective or that my feature works