Fix remote GPIO hang on macOS

[ralphweng2023]

Description

Fixes the issue where remote_raspi_init hangs indefinitely on macOS when trying to connect to a remote Raspberry Pi.

Root Cause: SDLNet_TCP_Open is a blocking function with no timeout. On macOS, when the host is unreachable, it hangs indefinitely (potentially for minutes due to OS-level TCP timeout settings).

Solution: Implement a non-blocking TCP connection with a 5-second timeout using native socket calls:

1. Create a non-blocking socket using fcntl()/ioctlsocket()
2. Initiate connection (returns immediately with EINPROGRESS)
3. Use select() with timeout to wait for connection
4. Check connection result with getsockopt(SO_ERROR)
5. If successful, close the test socket and use SDLNet_TCP_Open (which now succeeds immediately)

Changes to network_driver.cpp:

• Added platform-specific includes for socket operations (fcntl.h, winsock2.h, etc.)
• Added SK_CONNECTION_TIMEOUT_SECONDS constant (5 seconds)
• Added _connect_with_timeout() helper function
• Modified sk_open_tcp_connection() to use timeout for client connections
• Server socket creation (host=null) still uses the original blocking method

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

Built and tested on macOS using CMake:

cd projects/cmake
cmake --preset macOS
cmake --build build/

cd ../../bin
./skunit_tests --order rand
# Result: All tests passed (1263 assertions in 79 test cases)

./skunit_tests "[networking]"
# Result: All tests passed (31 assertions in 2 test cases)

Testing Checklist

• Code compiles without errors on macOS
• All existing unit tests pass (79 test cases)
• All networking tests pass (31 assertions)
• Connection timeout works correctly (5 second limit)
• Tested on Linux/WSL (not available on this machine)
• Tested on Windows/MSYS2 (not available on this machine)

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code in hard-to-understand areas
• My changes generate no new warnings
• Existing tests continue to pass
• The fix is backward compatible with existing code