Apply same performance optimizations to wsssh C version as wsscp

- Replace blocking recv() with select() for efficient I/O multiplexing
- Add 50ms timeouts to prevent indefinite blocking operations
- Increase buffer size from 4KB to 1MB for optimal throughput
- Add 3-second exit delay after SSH completion for clean shutdown
- Fix setup_tunnel return codes to prevent segmentation faults
- Correct memory management in argument cleanup