Add Ratatui apps over SSH to examples

[ricott1]

We could add some minimal examples on how to serve a ratatui app over SSH. After running the example, connect the clients by running ssh localhost -p 2222.

The ratatui_app.rs example serves a separate app instance to each client, which can be checked by connecting 2 clients and trying to reset the app counter by pressing c. Each app counter should update independently.

The ratatui_shared_app.rs example serves the same app instance to each client, which can be checked by connecting 2 clients and trying to reset the app counter by pressing c. Each client should see the app counter update at the same time. This example can be used to build something along the lines of sshtron.

I also update the toolchain file to fix a build error, let me know if you prefer to have that committed to a separate PR.

[ricott1]

The unsuccessful check is an unrelated clippy issue

[Eugeny]

Thank you, merged!