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/daemon/openrpc.rs

@@ -23,11 +23,6 @@ use serde_json::{Value, json};
 /// `components/schemas`, the same place OpenAPI does.
 const DEFINITIONS_PATH: &str = "#/components/schemas/";
 
-/// A method that takes no parameters.
-fn nothing() -> Value {
-    json!({ "type": "null" })
-}
-
 fn schema_of<T: JsonSchema>(generator: &mut SchemaGenerator) -> Value {
     generator.subschema_for::<T>().to_value()
 }
@@ -60,6 +55,7 @@ fn params_schema(method: Method, generator: &mut SchemaGenerator) -> Value {
             schema_of::<UserRef>(generator)
         }
         Method::SharesSet => schema_of::<DirectoriesParams>(generator),
+        // Methods that take no parameters.
         Method::DaemonStatus
         | Method::DaemonStop
         | Method::RpcDiscover
@@ -72,7 +68,7 @@ fn params_schema(method: Method, generator: &mut SchemaGenerator) -> Value {
         | Method::MessageHistory
         | Method::SearchList
         | Method::SharesStatusOf
-        | Method::SharesReindex => nothing(),
+        | Method::SharesReindex => json!({ "type": "null" }),
     }
 }