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/peer/file_search_response.rs

@@ -9,9 +9,9 @@ impl MessageHandler<PeerMessage> for FileSearchResponse {
         9
     }
     fn handle(&self, message: &mut Message, sender: Sender<PeerMessage>) {
-        let file_search = match SearchResult::new_from_message(message) {
-            Ok(result) => result,
-            Err(_) => return, // Skip malformed search results
+        // Skip malformed search results
+        let Ok(file_search) = SearchResult::new_from_message(message) else {
+            return;
         };
 
         sender