🔧 Fix all unused_mut warnings: 16 instances cleaned up

- Remove unnecessary 'mut' from variable declarations
- Clean up code in boxes/, interpreter/, mir/, backend/, and runtime/
- No functional changes, just cleaner code

src/boxes/aot_compiler_box.rs

@@ -31,7 +31,7 @@ impl AotCompilerBox {
             Err(e) => return Box::new(StringBox::new(format!("ERR: current_exe(): {}", e)))
         };
         // Propagate relevant envs (AOT/JIT observe)
-        let mut c = cmd.arg("--backend").arg("vm") // ensures runner path
+        let c = cmd.arg("--backend").arg("vm") // ensures runner path
                       .arg("--compile-native")
                       .arg("-o").arg(out)
                       .arg(file)

src/boxes/p2p_box.rs

@@ -108,7 +108,7 @@ impl P2PBox {
         // Create transport and attach receive callback before boxing
         let (transport_boxed, attach_cb): (Box<dyn Transport>, bool) = match transport_kind {
             TransportKind::InProcess => {
-                let mut t = InProcessTransport::new(node_id.clone());
+                let t = InProcessTransport::new(node_id.clone());
                 // We'll attach callback below after P2PBox struct is created
                 (Box::new(t), true)
             }

src/boxes/socket_box.rs

@@ -215,7 +215,7 @@ impl SocketBox {
         if ms == 0 { return self.accept(); }
 
         let start = std::time::Instant::now();
-        if let Ok(mut guard) = self.listener.write() {
+        if let Ok(guard) = self.listener.write() {
             if let Some(ref listener) = *guard {
                 let _ = listener.set_nonblocking(true);
                 loop {
@@ -319,7 +319,7 @@ impl SocketBox {
         let stream_guard = self.stream.write().unwrap();
         if let Some(ref stream) = *stream_guard {
             match stream.try_clone() {
-                Ok(mut stream_clone) => {
+                Ok(stream_clone) => {
                     drop(stream_guard);
                     let _ = stream_clone.set_read_timeout(Some(Duration::from_millis(ms)));
                     let mut reader = BufReader::new(stream_clone);