Avoid panics returning error instead

[dimartiro]

Description

Improve robustness by replacing .expect() calls with proper error handling in opening.rs.

Instead of panicking when on_noise_channel_open() or on_noise_channel_data() fail, the errors are now logged and the connection is gracefully closed by returning WebRtcEvent::ConnectionClosed

Closes #350
Closes ChainSafe/gossamer-parity#77

[haikoschol]

lgtm. @dimartiro where these the only places in the webrtc implementation that use expect(), unwrap(), etc? I understood the issue more general than just being about opening.rs and IIRC there are more places that need proper error handling. Having said that, having many small PRs is probably a good approach either way.

[dimartiro]

lgtm. @dimartiro where these the only places in the webrtc implementation that use expect(), unwrap(), etc? I understood the issue more general than just being about opening.rs and IIRC there are more places that need proper error handling. Having said that, having many small PRs is probably a good approach either way.

Thanks for the review!
So far, these are the ones annotated with the issue in the comments. I'm not too familiar with the code yet, but I'll take a look and check if there are more places where this change might apply

[lexnv]

Looks good to me! I would keep the issues open until we sort out all the places we might panic 🙏