core/muxing: Generalise `StreamMuxer::poll_address_change` to `poll`

[thomaseizinger]

Description

This is to allow general-purpose background work to be performed by implementations.

Links to any relevant issues

https://github.com/libp2p/rust-libp2p/issues/2722

Open Questions

Change checklist

• [x] I have performed a self-review of my own code
• [x] I have made corresponding changes to the documentation ~- [ ] 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