fix: resolve clippy warnings

Reduce clippy warnings from54 to16 by fixing mechanical issues:

- collapsible_if: collapse nested if-let chains with let-chains
- clone_on_copy: remove unnecessary .clone() on Copy types
- manual_clamp: replace .max().min() with .clamp()
- unnecessary_cast: remove redundant type casts
- collapsible_else_if: flatten else-if chains
- contains_vs_iter_any: replace .iter().any() with .contains()
- unnecessary_closure: replace .or_else(|| x) with .or(x)
- useless_conversion: remove redundant .into() calls
- is_none_or: replace .map_or(true, ...) with .is_none_or(...)
- while_let_loop: convert loop with if-let-break to while-let

Remaining16 warnings are design-level issues (too_many_arguments,
await_holding_lock, type_complexity, new_ret_no_self) that require
architectural changes to fix.

src/transport/middle_proxy/send.rs

@@ -242,10 +242,10 @@ impl MePool {
             }
             if preferred.is_empty() {
                 let def = self.default_dc.load(Ordering::Relaxed);
-                if def != 0 {
-                    if let Some(v) = map_guard.get(&def) {
-                        preferred.extend(v.iter().map(|(ip, port)| SocketAddr::new(*ip, *port)));
-                    }
+                if def != 0
+                    && let Some(v) = map_guard.get(&def)
+                {
+                    preferred.extend(v.iter().map(|(ip, port)| SocketAddr::new(*ip, *port)));
                 }
             }
 
@@ -267,7 +267,7 @@ impl MePool {
             if !self.writer_accepts_new_binding(w) {
                 continue;
             }
-            if preferred.iter().any(|p| *p == w.addr) {
+            if preferred.contains(&w.addr) {
                 out.push(idx);
             }
         }