fix(ci): resolve test compilation warnings on non-Linux platforms

- Move ctx variable inside #[cfg(target_os = "linux")] block in
  test_completion_result_types() to avoid unused variable warning
- Add separate #[cfg(not(target_os = "linux"))] block for non-Linux
  platforms with prefixed _ctx variable
- Addresses CI failures on Windows and macOS builds

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: doublegate

crates/wraith-transport/src/io_uring.rs

@@ -568,10 +568,9 @@ mod tests {
 
     #[test]
     fn test_completion_result_types() {
-        let mut ctx = IoUringContext::new(64).unwrap();
-
         #[cfg(target_os = "linux")]
         {
+            let mut ctx = IoUringContext::new(64).unwrap();
             ctx.submit_read(1, 0, 1024).unwrap();
             ctx.submit_write(2, 0, &[0u8; 2048]).unwrap();
             ctx.submit_fsync(3).unwrap();
@@ -587,5 +586,11 @@ mod tests {
                 }
             }
         }
+
+        // On non-Linux, just verify the stub context works
+        #[cfg(not(target_os = "linux"))]
+        {
+            let _ctx = IoUringContext::new(64).unwrap();
+        }
     }
 }