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/crypto/random.rs

@@ -95,7 +95,7 @@ impl SecureRandom {
             return 0;
         }
         
-        let bytes_needed = (k + 7) / 8;
+        let bytes_needed = k.div_ceil(8);
         let bytes = self.bytes(bytes_needed.min(8));
         
         let mut result = 0u64;