Refactor vpnLogger to fix thread ownership issues and improve robustness.

- Move QProcess reading to the correct thread to prevent ring buffer corruption and potential crashes (PR #207).
- Replace `QThread::msleep` with a non-blocking coalescing timer for efficient data handling, reducing the risk of lost prompt matches (e.g., issue #166).
- Clean up unused signals and ensure proper resource teardown (`procFinished` clears maps and closes log files).
- Enhance test `90_gui.sh` to validate resilience to high-output child processes, ensuring the GUI remains stable and no output is lost.
- Remove redundant `vpnLogger::finished()` connects that emitted errors on start.