style: crank clippy to pedantic+nursery and fix all lints

Enable the full clippy all + pedantic + nursery groups as workspace warnings,
with a small documented allow-list for the pedantic/nursery lints this project
intentionally does not follow (rustdoc-style requirements, deliberate numeric
casts in the protocol/UI layers, and a few noisy nursery lints). Also enable
the rust unused_lifetimes and unsafe_op_in_unsafe_fn lints.

Fixed every resulting warning (527 -> 0) mechanically per clippy's suggestions:
inline format args, const fns, item ordering, let-else, redundant clones,
map_or, cast_lossless, Eq derives, associated-fn conversions for methods that
never used self, and removing unnecessary Result wrappers whose call sites could
never propagate an error. No runtime behavior changed; cargo fmt applied.

cargo clippy --workspace --all-targets: 0 warnings. All tests pass.

soulseek-rs-lib/src/message/server/get_peer_address.rs

@@ -22,7 +22,7 @@ impl MessageHandler<ServerMessage> for GetPeerAddressHandler {
         let port = message.read_int32();
         let obfuscation_type = message.read_int32();
         let obfuscated_port = message.read_int32() as u16;
-        println!("GetPeerAddressHandler: {:?}", username); // Debug print
+        println!("GetPeerAddressHandler: {username:?}"); // Debug print
 
         sender
             .send(ServerMessage::GetPeerAddressResponse {