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/network/probe.rs

@@ -95,23 +95,21 @@ pub async fn run_probe(config: &NetworkConfig, stun_addr: Option<String>, nat_pr
 }
 
 pub fn decide_network_capabilities(config: &NetworkConfig, probe: &NetworkProbe) -> NetworkDecision {
-    let mut decision = NetworkDecision::default();
+    let ipv4_dc = config.ipv4 && probe.detected_ipv4.is_some();
+    let ipv6_dc = config.ipv6.unwrap_or(probe.detected_ipv6.is_some()) && probe.detected_ipv6.is_some();
 
-    decision.ipv4_dc = config.ipv4 && probe.detected_ipv4.is_some();
-    decision.ipv6_dc = config.ipv6.unwrap_or(probe.detected_ipv6.is_some()) && probe.detected_ipv6.is_some();
-
-    decision.ipv4_me = config.ipv4
+    let ipv4_me = config.ipv4
         && probe.detected_ipv4.is_some()
         && (!probe.ipv4_is_bogon || probe.reflected_ipv4.is_some());
 
     let ipv6_enabled = config.ipv6.unwrap_or(probe.detected_ipv6.is_some());
-    decision.ipv6_me = ipv6_enabled
+    let ipv6_me = ipv6_enabled
         && probe.detected_ipv6.is_some()
         && (!probe.ipv6_is_bogon || probe.reflected_ipv6.is_some());
 
-    decision.effective_prefer = match config.prefer {
-        6 if decision.ipv6_me || decision.ipv6_dc => 6,
-        4 if decision.ipv4_me || decision.ipv4_dc => 4,
+    let effective_prefer = match config.prefer {
+        6 if ipv6_me || ipv6_dc => 6,
+        4 if ipv4_me || ipv4_dc => 4,
         6 => {
             warn!("prefer=6 requested but IPv6 unavailable; falling back to IPv4");
             4
@@ -119,10 +117,17 @@ pub fn decide_network_capabilities(config: &NetworkConfig, probe: &NetworkProbe)
         _ => 4,
     };
 
-    let me_families = decision.ipv4_me as u8 + decision.ipv6_me as u8;
-    decision.effective_multipath = config.multipath && me_families >= 2;
+    let me_families = ipv4_me as u8 + ipv6_me as u8;
+    let effective_multipath = config.multipath && me_families >= 2;
 
-    decision
+    NetworkDecision {
+        ipv4_dc,
+        ipv6_dc,
+        ipv4_me,
+        ipv6_me,
+        effective_prefer,
+        effective_multipath,
+    }
 }
 
 fn detect_local_ip_v4() -> Option<Ipv4Addr> {

src/network/stun.rs

@@ -198,16 +198,11 @@ async fn resolve_stun_addr(stun_addr: &str, family: IpFamily) -> Result<Option<S
         });
     }
 
-    let addrs = lookup_host(stun_addr)
+    let mut addrs = lookup_host(stun_addr)
         .await
         .map_err(|e| ProxyError::Proxy(format!("STUN resolve failed: {e}")))?;
 
     let target = addrs
-        .filter(|a| match (a.is_ipv4(), family) {
-            (true, IpFamily::V4) => true,
-            (false, IpFamily::V6) => true,
-            _ => false,
-        })
-        .next();
+        .find(|a| matches!((a.is_ipv4(), family), (true, IpFamily::V4) | (false, IpFamily::V6)));
     Ok(target)
 }