require valid Url, implement magnet links

src/config.rs

@@ -3,6 +3,7 @@ use std::{
     net::{Ipv4Addr, SocketAddr, SocketAddrV4},
     path::PathBuf,
 };
+use url::Url;
 
 #[derive(Parser, Debug)]
 #[command(version, about, long_about = None)]
@@ -13,7 +14,7 @@ pub struct Config {
 
     /// Tracker(s) to join / scrape requests
     #[arg(short, long)]
-    pub tracker: Option<Vec<String>>,
+    pub tracker: Option<Vec<Url>>,
 
     /// Bind server `host:port` to listen incoming connections on it
     #[arg(short, long, default_value_t = SocketAddr::V4(SocketAddrV4::new(Ipv4Addr::LOCALHOST, 1965)))]