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/src/commands/social.rs

@@ -39,17 +39,13 @@ pub fn fetch_listing(
         CliError::connection(format!("cannot ask {user} for a listing: {e}"))
     })?;
 
-    let deadline = Instant::now() + timeout;
-    while Instant::now() < deadline {
-        if let Some(directories) = client.take_browse_result(user) {
-            return Ok(directories);
-        }
-        std::thread::sleep(POLL);
-    }
-    Err(CliError::timeout(format!(
-        "{user} did not send a file list within {}s",
-        timeout.as_secs()
-    )))
+    super::poll_until(timeout, POLL, || client.take_browse_result(user))
+        .ok_or_else(|| {
+            CliError::timeout(format!(
+                "{user} did not send a file list within {}s",
+                timeout.as_secs()
+            ))
+        })
 }
 
 pub fn browse(ctx: &Ctx, args: &BrowseArgs) -> CliResult {
@@ -143,22 +139,18 @@ pub fn room_users(ctx: &Ctx, room: &str, timeout: Duration) -> CliResult {
     ctx.out
         .status(&format!("waiting for {room}'s member list…"));
 
-    let deadline = Instant::now() + timeout;
-    let mut members = Vec::new();
-    while Instant::now() < deadline && members.is_empty() {
-        members = session.client.room_members(room);
-        if members.is_empty() {
-            std::thread::sleep(POLL);
-        }
-    }
+    let listed = super::poll_until(timeout, POLL, || {
+        let members = session.client.room_members(room);
+        (!members.is_empty()).then_some(members)
+    });
     let _ = session.client.leave_room(room);
 
-    if members.is_empty() {
+    let Some(members) = listed else {
         return Err(CliError::timeout(format!(
             "{room} sent no member list within {}s",
             timeout.as_secs()
         )));
-    }
+    };
     for user in members {
         ctx.out.emit(&RoomMemberRecord {
             room: room.to_string(),