Feat/persistency import export

[viktorbeck98]

feat: export and import EventPersistency state on demand

Problem

There was no way to transfer a detector's trained state between environments (e.g. training → production) or take a manual snapshot outside the auto-save timer cycle, without constructing a full PersistencySaver with its threading machinery.

What changed

Layer 1 — standalone functions (detectmatelibrary.utils.persistency)

save and load are extracted from PersistencySaver's internals and exposed as module-level functions. PersistencySaver now delegates to them, so the serialisation format lives in exactly one place.

Layer 2 — detector-level wrappers (CoreDetector)

export_state and import_state are thin wrappers around the above. import_state is thread-safe: it acquires the saver lock before loading when a PersistencySaver is running.

Bytes overload

Both layers accept an optional path. When omitted, save/export_state return the state as an in-memory zip archive (bytes); load/import_state accept either a path string or those bytes. This lets an API send or receive state without touching the filesystem.

Metadata

event_data_class is now written to the metadata JSON and restored on load, so a detector loaded into a fresh EventPersistency picks the correct backend for new events automatically. Existing snapshots without the field continue to load fine.

Usage

# File-based (unchanged behaviour)
detector.export_state("s3://bucket/snapshots/my-detector")
detector.import_state("s3://bucket/snapshots/my-detector")

# Bytes-based (new — no disk I/O)
data: bytes = detector.export_state()
detector.import_state(data)

# Standalone (advanced / no detector)
from detectmatelibrary.utils import persistency
data = persistency.save(ep)
persistency.load(ep, data)

What did not change

• PersistencySaver public API (save, load, start, stop) is unchanged.
• On-disk format is unchanged; one new optional metadata field added, old snapshots remain loadable.
• EventPersistency gains no new public methods.

Tests

• TestStandaloneSaveLoad — 7 new tests covering the bytes overload roundtrip
• TestDetectorExportImportState — 3 new tests covering bytes export/import at the detector level, including a running-saver safety check