fix: survive busy sessions without exhausting file descriptors

The peer listener died with "Too many open files (os error 24)" on any
long-lived non-daemon session: only the daemon raised RLIMIT_NOFILE, and
peer sockets were unbounded — no idle reaping, no deadlines on accepted
transfer streams, and one peer could hold two connections under split
registry identities.

- raise the open-file limit at the top of run(), for every entry point,
  and warn from Client::connect when the soft limit is below 1024
- reap peer control connections idle for five minutes; a clean
  disconnect no longer discards the peer's queued uploads
- give listener-supplied download streams and upload serving the same
  read/write deadlines dialled sockets already had
- register inbound peers under their plain username so the registry
  holds one connection per peer, and announce them like pierced ones
- hold the registry lock across actor spawn + insert and surface
  thread-spawn failure, so an instantly-dead peer cannot leave a
  zombie entry

soulseek-rs-lib/tests/e2e.rs

@@ -734,14 +734,14 @@ fn a_file_downloads_from_a_peer_over_p_and_f_connections() {
         .recv_timeout(Duration::from_secs(5))
         .expect("mock uploader P connection");
 
-    // The listener registers an incoming peer under "<username>:direct"; give
+    // The listener registers an incoming peer under its plain username; give
     // that registration a moment to complete before queuing the download.
     std::thread::sleep(Duration::from_millis(1500));
 
     let (_download, status_rx) = client
         .download(
             filename.to_string(),
-            "e2e_mockpeer:direct".to_string(),
+            "e2e_mockpeer".to_string(),
             size,
             download_dir.display().to_string(),
         )
@@ -811,7 +811,7 @@ fn an_interrupted_download_resumes_from_its_partial_file() {
     let (_download, status_rx) = client
         .download(
             filename.to_string(),
-            "e2e_resume_peer:direct".to_string(),
+            "e2e_resume_peer".to_string(),
             size,
             download_dir.display().to_string(),
         )