The changes in this commit are all intertwined and it was hard to
split them into smaller commits:
* Use custom transports everywhere
Instead of `file://` and instead of using a child process for fetching
and pushing; we go through our custom transports, which use the `rad://`
and `heartwood://` schemes.
* Introduce a 'mock' remote transport
To test the remote transport without needing to spawn TCP streams,
we add a mock transport that works between storages on the file
system.
* Get rid of node's `git-url`
Instead of git urls, nodes simply use their node-ids to replicate.
This type that was wrapping `Message` isn't very useful here.
If we decide that we do need something like that, it's best handled one
layer below.
Signed-off-by: Alexis Sellier <alexis@radicle.xyz>
Alexis Sellier