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/api.rs

@@ -149,8 +149,11 @@ pub trait SessionApi: Send + Sync {
         Vec::new()
     }
 
+    // aislop-ignore-next-line complexity/function-too-long -- scanner bug: a bodyless trait signature followed only by more signatures has no closing brace, so the counter runs to EOF. One line.
     fn shared_counts(&self) -> (u32, u32);
+    // aislop-ignore-next-line complexity/function-too-long -- same scanner bug: bodyless signature measured to EOF. One line.
     fn shared_directories(&self) -> Vec<String>;
+    // aislop-ignore-next-line complexity/function-too-long -- same scanner bug: bodyless signature measured to EOF. One line.
     fn set_shared_directories(&self, directories: Vec<String>) -> Result<()>;
 
     /// Point future transfers at `directory`.
@@ -158,6 +161,7 @@ pub trait SessionApi: Send + Sync {
     /// Only a daemon holds a download folder of its own — locally every
     /// download call names its directory, so the local session has nothing to
     /// store and accepts silently.
+    // aislop-ignore-next-line complexity/function-too-long -- same scanner bug: bodyless signature measured to EOF. One line.
     fn set_download_directory(&self, directory: String) -> Result<()>;
 }