Implement the REST api

[Andrewsooter442]

No description provided.

[4adex]

Also add exhaustive tests for the server, and move the api_server to a new directory named clients at the hierarchy of crates. All clients will go in that directory

[4adex]

 let listener = TcpListener::bind(config.listen_addr)
        .await
        .map_err(|e| ..)?;
    axum::serve(listener, app.into_make_service())
        .await
        .map_err(|e| ..)?;

Here map the errors and pass them gracefully instead of using unwraps,
define new error types if you want. Also this might be independent of core crates so you need to define different error type.

[4adex]

Else looks good