fix(session): replace internal header include with forward declaration (#943)

messaging_session.h included internal/tcp/tcp_socket.h which is not
installed by cmake. External consumers (e.g., pacs_system) that
transitively include this header get a fatal compilation error.

Replace with a forward declaration of kcenon::network::internal::tcp_socket
since the header only uses std::shared_ptr<tcp_socket> as a member type.
Move the actual include to messaging_session.cpp where the full type is needed.

Closes #942

Author: kcenon

include/kcenon/network/detail/session/messaging_session.h

@@ -32,7 +32,11 @@
 #include <asio.hpp>
 
 #include "kcenon/network/interfaces/i_session.h"
-#include "internal/tcp/tcp_socket.h"
+
+namespace kcenon::network::internal
+{
+	class tcp_socket;
+}
 
 // Use nested namespace definition in C++17
 namespace kcenon::network::session

src/session/messaging_session.cpp

@@ -6,6 +6,7 @@
 
 #include <span>
 
+#include "internal/tcp/tcp_socket.h"
 #include "internal/integration/logger_integration.h"
 #include "kcenon/network/detail/metrics/network_metrics.h"