Add unit tests for core messaging and WebSocket modules

[kcenon]

What

Add dedicated unit tests for 8 untested modules: core messaging (6) and HTTP/WebSocket (2). Part of #953.

Scope

Category	Modules	Files
Core Messaging	6	messaging_client.cpp, messaging_server.cpp, messaging_udp_client.cpp, messaging_udp_server.cpp, secure_messaging_udp_client.cpp, secure_messaging_udp_server.cpp
HTTP/WebSocket	2	websocket_client.cpp, websocket_server.cpp

Why

• Core messaging modules are the primary user-facing networking APIs with 0% dedicated test coverage
• WebSocket client/server lack unit tests despite being production-ready features
• These modules handle connection lifecycle, message routing, and error handling — high regression risk
• Part of epic Expand unit test coverage from 40% to 80% #953 to raise coverage from 48% to 80%

Where

• Source: src/core/, src/http/
• Tests: tests/unit/ (new test files)
• CMake: tests/CMakeLists.txt (register new tests)

How

Technical Approach

1. Create unit test files following existing patterns (see secure_messaging_client_test.cpp as reference)
2. Use GTest with mock/stub patterns for network I/O where needed
3. Test construction, configuration, connection lifecycle, and error paths
4. Register tests in tests/CMakeLists.txt

Acceptance Criteria

• All 8 modules have dedicated unit test files
• Tests pass on local build
• No GTEST_SKIP() markers
• Tests cover constructors, public methods, and error handling

[kcenon]

Implementation Update

Field	Value
PR	#970
Branch	feat/issue-966-add-core-messaging-websocket-tests
Status	In Review

Summary

Added 8 dedicated unit test files covering all modules specified in this issue:

• Core Messaging: messaging_client, messaging_server, messaging_udp_client/server, secure_messaging_udp_client/server
• WebSocket: messaging_ws_client, messaging_ws_server

Also introduced add_network_test() CMake macro to reduce per-target boilerplate.