auto_load true start without saved state on first boot

[thorinaboenke]

Task

#178

Description

Catch PersistencyLoadError during the auto-load init and log an info message instead of raising:

How Has This Been Tested?

new unit test in detectmatelibrary_tests/test_utils/test_persistency_saver.py

Manual end-to-end test (Docker Compose getting-started setup in DetectMateService) on branch https://github.com/ait-detectmate/DetectMateService/tree/feature/persistency-admin-endpoints

1. Added persist: { path: /state, auto_load: true } to container/config/detector_config.yaml with no prior saved state.
2. Started the stack, detector came up cleanly. /admin/persistency/status returned events_seen_count: 0, last_saved_at: null, confirming the first-boot path no longer crashes.
3. Sent two nginx requests (/hello, /world) to feed training data. Status showed events_seen_count: 2, events_since_save: 4
4. Called POST /admin/persistency/save. Response {"message": "state saved"}. State files confirmed on disk (metadata.json + *.msgpack). Status showed events_since_save: 0 and last_saved_at populated.
5. Restarted the detector container (docker compose restart detector). After startup, status showed events_seen_count: 2, events_with_data_count: 1. state fully restored via auto_load on restart.

Checklist

• This Pull-Request goes to the development branch.
• I have successfully run prek locally.
• I have added tests to cover my changes.
• I have linked the issue-id to the task-description.
• I have performed a self-review of my own code.