Remove the concept of individual `Transport::Listener` streams from `Transport`.
Instead the `Transport` is polled directly via `Transport::poll`. The
`Transport` is now responsible for driving its listeners.
This commit adds an implementation for the circuit relay v2 protocol to be used
as a relay server, i.e. it supports incoming HOP requests and outgoing STOP
requests and used as a relay clients, i.e. outgoing HOP requests and incoming
STOP requests.
The existing circuit relay v1 protocol implementation is moved to
protocols/relay/src/v1.
Co-authored-by: ronzigelman <ronzigelman@gmail.com>
Co-authored-by: Marco Munizaga <git@marcopolo.io>
Co-authored-by: Thomas Eizinger <thomas@eizinger.io>
Co-authored-by: Elena Frank <57632201+elenaf9@users.noreply.github.com>
