fix(lib): advertise real slot, speed and queue figures in search replies

Every reply to a peer's search claimed a free upload slot, no speed and
an empty queue, whatever the sharer was doing, and searchers rank
sources on exactly those fields. A reply now says whether a slot is
free, the bytes per second of the last completed upload, and how many
uploads are waiting.

soulseek-rs-lib/examples/stress.rs

@@ -415,7 +415,7 @@ impl SeederState {
             })
             .collect();
         let response =
-            build_file_search_response(&self.name, token, &entries, 1, 0);
+            build_file_search_response(&self.name, token, &entries, 1, 0, 0);
 
         let Ok(mut guard) = self.conn.lock() else {
             return;