Basler backend: device discovery & fixes

Refactor and harden BaslerCameraBackend: add a basler namespace view/ensure helpers, stable device_id (serial) handling with legacy fallbacks, and persistence of device identity. Introduce fast_start probe mode to avoid starting acquisition/creating converter, and an apply_transforms option to perform rotation/crop in read().

Add testable device enumeration helpers ( _enumerate_devices_cls, discover_devices, get_device_count, quick_ping ) and utility operations (rebind_settings, sanitize_for_probe) to improve discovery, rebinding, and fast probing. Improve open()/read()/close() with safer node access, better logging, explicit handling of exposure/gain/fps, resolution snapping to node increments/ranges, read-back of actual telemetry, and clearer errors when operating in fast-start probe mode. Maintain backward compatibility with legacy properties (serial, resolution) while preferring namespaced options.

Author: C-Achard