improvement: add NostrRepo trait, with sqlite implementation

This is inspired by the work of
v0l (https://github.com/v0l/nostr-rs-relay/).

A new trait abstracts the storage layer with an async API.  Rusqlite
is still used with worker threads, but this allows for Postgresql or
other backends to be used.

There may be bugs, this has not been rigorously tested.

src/main.rs

@@ -1,6 +1,6 @@
 //! Server process
 use clap::Parser;
-use nostr_rs_relay::cli::*;
+use nostr_rs_relay::cli::CLIArgs;
 use nostr_rs_relay::config;
 use nostr_rs_relay::server::start_server;
 use std::sync::mpsc as syncmpsc;
@@ -37,12 +37,15 @@ fn main() {
     if let Some(db_dir) = db_dir_arg {
         settings.database.data_directory = db_dir;
     }
+    // we should have a 'control plane' channel to monitor and bump
+    // the server.  this will let us do stuff like clear the database,
+    // shutdown, etc.; for now all this does is initiate shutdown if
+    // `()` is sent.  This will change in the future, this is just a
+    // stopgap to shutdown the relay when it is used as a library.
     let (_, ctrl_rx): (MpscSender<()>, MpscReceiver<()>) = syncmpsc::channel();
     // run this in a new thread
-    let handle = thread::spawn(|| {
-        // we should have a 'control plane' channel to monitor and bump the server.
-        // this will let us do stuff like clear the database, shutdown, etc.
-        let _svr = start_server(settings, ctrl_rx);
+    let handle = thread::spawn(move || {
+        let _svr = start_server(&settings, ctrl_rx);
     });
     // block on nostr thread to finish.
     handle.join().unwrap();