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/peer/mod.rs

@@ -10,33 +10,7 @@ pub use download_peer::DownloadPeer;
 
 use crate::message::Message;
 use core::fmt;
-use std::{net::TcpStream, str::FromStr};
-
-#[derive(Debug)]
-#[allow(dead_code)]
-pub struct NewPeer {
-    pub username: String,
-    pub connection_type: ConnectionType,
-    pub token: u32,
-    pub tcp_stream: TcpStream,
-}
-impl NewPeer {
-    pub fn new_from_message(
-        message: &mut Message,
-        tcp_stream: TcpStream,
-    ) -> Option<Self> {
-        let username = message.read_string();
-        let connection_type = message.read_string().parse().ok()?;
-        let token = message.read_int32();
-
-        Some(Self {
-            username,
-            connection_type,
-            token,
-            tcp_stream,
-        })
-    }
-}
+use std::str::FromStr;
 
 #[derive(Debug, Clone)]
 pub enum ConnectionType {
@@ -81,7 +55,6 @@ impl fmt::Display for ConnectionType {
 }
 
 #[derive(Debug, Clone)]
-#[allow(dead_code)]
 pub struct Peer {
     pub username: String,
     pub connection_type: ConnectionType,
@@ -93,7 +66,7 @@ pub struct Peer {
     pub obfuscated_port: Option<u16>,
 }
 impl Peer {
-    #[allow(clippy::too_many_arguments, dead_code)]
+    #[allow(clippy::too_many_arguments)]
     #[must_use]
     pub const fn new(
         username: String,
@@ -116,7 +89,6 @@ impl Peer {
             obfuscated_port: Some(obfuscated_port),
         }
     }
-    #[allow(dead_code)]
     pub fn new_from_message(message: &mut Message) -> Option<Self> {
         let username = message.read_string();
         // The connection type is an untrusted string; an unknown value must not