chore: remove dead code and stale comments

- Drop dead Rooms/Room infrastructure and the rooms field on Context.
- Remove unused ActorMessage::Tick variant and the now-empty handler arm.
- Strip dead active-thread tracking machinery from ThreadPool (unused
  getters, _id/_active_threads/_total_threads parameters).
- Flatten ServerActor::initiate_connection: the duplicated retry block
  was a copy-paste retry against the same address with the same args
  and could never succeed where the first attempt failed.
- Delete commented-out print_hex2/decode debug stubs, dead test
  fixtures in login.rs and message_user.rs, the 47-line commented body
  of RoomListHandler, and assorted // TODO theater.

soulseek-rs-lib/src/message/server/message_factory.rs

@@ -106,7 +106,6 @@ impl MessageFactory {
             .write_int32(41)
             .write_int32(transfer.token)
             .write_bool(true)
-            // .write_int64(transfer.size)
             .clone()
     }
     pub fn build_pierce_firewall_message(token: u32) -> Message {
@@ -154,8 +153,6 @@ fn test_build_login_message() {
     ]
     .to_vec();
 
-    // println!("{:?}", print_hex(message.get_data()));
-    // assert_eq!(expect, message.get_data());
     assert_eq!(expect, message.get_data())
 }