feat(libp2p-swarm-test): Support `tokio`

[ark0f]

Description

Notes & open questions

Change checklist

• [x] I have performed a self-review of my own code
• [x] I have made corresponding changes to the documentation
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] A changelog entry has been made in the appropriate crates

[guillaumemichel]

I agree with @jxs, IMO async-std should be replaced by tokio.

[dariusc93]

I do agree with the idea of replacing async-std with tokio as well. Maybe start with the tests and following #4449 we can move on to preferring tokio in other parts of rust-libp2p.

[ark0f]

Done by #5551