fix(async): remove unused io_context reference from asio_net_service

- remove unused private field ctx_ to eliminate -Wunused-private-field warning
- simplify constructor by removing unnecessary member initialization
- keep API consistent while aligning implementation with actual usage

improves design clarity and ensures clean build with strict warnings

Author: GaspardKirira

src/net/asio_net_service.cpp

@@ -20,8 +20,7 @@
 namespace vix::async::net::detail
 {
 
-  asio_net_service::asio_net_service(vix::async::core::io_context &ctx)
-      : ctx_(ctx)
+  asio_net_service::asio_net_service(vix::async::core::io_context &)
   {
     guard_ = std::make_unique<guard_t>(asio::make_work_guard(ioc_));
 

src/net/asio_net_service.hpp

@@ -43,7 +43,6 @@ namespace vix::async::net::detail
     void stop() noexcept;
 
   private:
-    vix::async::core::io_context &ctx_;
     asio::io_context ioc_;
     std::unique_ptr<guard_t> guard_;
     std::thread net_thread_;