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/bin/bulkloader.rs

@@ -1,14 +1,13 @@
 use std::io;
 use std::path::Path;
 use nostr_rs_relay::utils::is_lower_hex;
-use tracing::*;
+use tracing::info;
 use nostr_rs_relay::config;
 use nostr_rs_relay::event::{Event,single_char_tagname};
 use nostr_rs_relay::error::{Error, Result};
-use nostr_rs_relay::db::build_pool;
-use nostr_rs_relay::schema::{curr_db_version, DB_VERSION};
+use nostr_rs_relay::repo::sqlite::{PooledConnection, build_pool};
+use nostr_rs_relay::repo::sqlite_migration::{curr_db_version, DB_VERSION};
 use rusqlite::{OpenFlags, Transaction};
-use nostr_rs_relay::db::PooledConnection;
 use std::sync::mpsc;
 use std::thread;
 use rusqlite::params;
@@ -67,7 +66,7 @@ pub fn main() -> Result<()> {
 	info!("finished parsing events");
 	event_tx.send(None).ok();
 	let ok: Result<()> = Ok(());
-        return ok;
+        ok
     });
     let mut conn: PooledConnection = pool.get()?;
     let mut events_read = 0;