## Issue Addressed
#1388 partially (eth2_libp2p & network)
## Proposed Changes
TLDR at the end
- *Complex types* are 3 on the handlers/Behaviours but the types are `Poll<ComplexType>` where `ComplexType` comes from the traits of libp2p. Those, I don't thing are worth an alias. A couple more were from using tokio combinators and were removed writing things the async way and using [`BoxFuture`](https://docs.rs/futures/0.3.5/futures/future/type.BoxFuture.html)
- The *cognitive complexity*.. I tried to address those before (they come from the poll functions too) and tbh they are cognitively simpler to understand the way they are now. Moving separate parts to functions doesn't add much since that code is not repeated and they all do early returns. If moved those returns would now need to be wrapped in an Option, probably, and checked to be returned again. I would leave them like that but that's just preference.
- *Too many arguments*: They are not easily put together in a wrapping struct since the parameters don't relate semantically (Ex: fn new with a log, a reference to the chain, a peer, etc) but some may differ.
- *Needless returns* were indeed needless
## Additional Info
TLDR: removed needless return, used BoxFuture and async, left the rest untouched since those lgtm
9ae9df806c