feat(echo): add echo client and server with CLI support

src/client/echo_client.hpp

@@ -0,0 +1,24 @@
+#pragma once
+
+#include "aliases.hpp"
+#include "logger.hpp"
+#include <string>
+
+class EchoClient final
+{
+  public:
+    EchoClient(IoContext &io, std::string host, unsigned short port);
+
+    bool run(const std::string &message);
+
+  private:
+    bool connect();
+    bool send(const std::string &message);
+    void close();
+
+  private:
+    IoContext &io_;
+    std::string host_;
+    unsigned short port_;
+    TcpSocket socket_{io_};
+};