This is a large change that introduces transport encryption via
a Noise_XK handshake. The inner `Service` now works directly
with `NodeId` and doesn't need to interact with socket addresses.
The transport logic takes place in `wire::transport`, and the
established sessions are passed down to `Service`.
Note that the i/o implementation in the `poll-reactor` crate still
needs testing, and there is still work to be done to integrate the
Git transport as part of this architecture.
Signed-off-by: Alexis Sellier <alexis@radicle.xyz>