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/stats/mod.rs

@@ -326,10 +326,10 @@ impl ReplayShard {
             
             // Use key.as_ref() to get &[u8] — avoids Borrow<Q> ambiguity
             // between Borrow<[u8]> and Borrow<Box<[u8]>>
-            if let Some(entry) = self.cache.peek(key.as_ref()) {
-                if entry.seq == queue_seq {
-                    self.cache.pop(key.as_ref());
-                }
+            if let Some(entry) = self.cache.peek(key.as_ref())
+                && entry.seq == queue_seq
+            {
+                self.cache.pop(key.as_ref());
             }
         }
     }