GenTL backend: device_id, discovery, and rebind

Add robust GenTL backend features: read backend options from properties["gentl"], support CTI search paths, and a fast_start probe mode that avoids starting acquisition. Introduce stable device identity handling (device_id with serial: and fp: formats) while keeping legacy serial/index fallbacks. Improve device selection logic (match device_id, exact/substring serial matching, index fallback) and persist discovered metadata back into settings. Add helpers: _device_id_from_info, discover_devices, rebind_settings, and quick_ping for reliable discovery/rebinding and UI integration. Make Harvester usage more defensive and handle different device_info shapes.

Author: C-Achard