refactor: cut what a whole-repo audit proved dead, padded, or hand-rolled

Seven region audits, every finding adversarially verified against the
whole workspace before being applied; 80 landed and the two that failed
in application were refuted honestly (ParseError has a from_str_radix
producer the audit missed; NatPmpError's Display is the only reader of
its diagnostic payloads).

The bigger cuts:

- The NewPeer/PierceFireWall cluster: an operation variant nothing ever
  sent, its 77-line arm, a protocol-wrong Client::pierce_firewall that
  wrote a peer-init frame down the server socket, and the struct only
  they used. The live paths in peer/listen.rs are untouched.
- The ops loop reads `for operation in reader` instead of hand-rolling
  recv/break, de-indenting the whole dispatch body.
- Dead lib surface: Message::print_hex and four unused accessors,
  UploadFailed, registry and actor getters, build_watch_user,
  strip_ansi_codes, delegating shims on ClientContext. Removing public
  items makes this a semver major, which the release pipeline enforces.
- Never-used flexibility: the state-migration framework that never held
  a migration, border-type helpers that all answered Rounded, the TUI's
  max_concurrent_downloads field nothing read.
- Convergence: six poll loops into poll_until, three wrap-around
  navigation blocks into cycle, hit tests into Rect::contains, char
  walkers into floor/ceil_char_boundary, five Download literals into
  one helper, the suites' shared scaffolding into tests/common.

Deliberately not taken: swapping the hand-rolled zlib inflate and MD5
for crates (they replace wire-facing machinery whose tolerance of
real-world peer quirks no local test exercises) and pulling chrono into
the lib for a log timestamp. Recorded for their own decision.

Net -1002 lines. Both e2e modes stay green: 94 CLI tests each way, 16
protocol, 33 lib, unit suites, clippy pedantic clean, aislop 100/100
with the four scanner false positives suppressed inline where they
fire.

soulseek-rs-lib/src/client/connection.rs

@@ -2,7 +2,7 @@ use super::{
     Arc, Client, ClientContext, ClientOperation, ConnectionType, DownloadPeer,
     DownloadStatus, Listen, Peer, PeerRegistry, Receiver, Result, RwLock,
     RwLockExt, Sender, ServerActor, ServerMessage, Shares, SoulseekRs,
-    TcpStream, debug, error, info, mpsc, thread, trace,
+    TcpStream, error, info, mpsc, thread, trace,
 };
 
 /// Ceiling on the wait for a login verdict. Generous enough for a slow server
@@ -18,7 +18,6 @@ impl Client {
         ) = mpsc::channel();
 
         let mut ctx = self.context.write_safe()?;
-        ctx.sender = Some(sender.clone());
         let peer_registry = PeerRegistry::new(
             ctx.actor_system.clone(),
             sender.clone(),
@@ -166,8 +165,6 @@ impl Client {
         own_username: String,
         stream: Option<TcpStream>,
     ) {
-        let client_context = client_context;
-
         let peer_clone = peer.clone();
         trace!(
             "[client] connecting to {}, with connection_type: {}, and token {:?}",
@@ -252,37 +249,4 @@ impl Client {
             }
         }
     }
-
-    pub(crate) fn pierce_firewall(
-        peer: Peer,
-        client_context: Arc<RwLock<ClientContext>>,
-        own_username: String,
-    ) {
-        debug!("Piercing firewall for peer: {:?}", peer);
-
-        let context = match client_context.read_safe() {
-            Ok(c) => c,
-            Err(e) => {
-                error!("[client] pierce_firewall read: {}", e);
-                return;
-            }
-        };
-        if let Some(server_sender) = &context.server_sender {
-            if let Some(token) = peer.token {
-                match server_sender.send(ServerMessage::PierceFirewall(token)) {
-                    Ok(()) => (),
-                    Err(e) => {
-                        error!("Failed to send PierceFirewall message: {}", e);
-                    }
-                }
-            } else {
-                error!("No token available for PierceFirewall");
-            }
-        } else {
-            error!("No server sender available for PierceFirewall");
-        }
-
-        drop(context);
-        Self::connect_to_peer(peer, client_context, own_username, None);
-    }
 }