exported zip has extra leading slash -> absolute paths in zip

[thorinaboenke]

Subject of the issue

The library's _save_to_bytes() (in DetectMateLibrary/src/detectmatelibrary/utils/persistency/persistency_saver.py) has an off-by-one when stripping the root prefix from fsspec MemoryFileSystem paths (paths start with /, file_path[len(root)+1:] leaves a stray leading slash.
The zip then contains /metadata.json and /events/1.msgpack instead of metadata.json and events/1.msgpack.

The library's own _load_from_bytes tolerates this (path joining absorbs the extra slash)
but if you download and then unzip you get absolute paths inside a zip (no valid archive layout)

Your environment

• Version of detectmate
• Version of python
• Docker or manual installation?

Steps to reproduce

from detectmatelibrary.detectors.new_value_detector import NewValueDetector, NewValueDetectorConfig

det = NewValueDetector(name="Demo", config=NewValueDetectorConfig(auto_config=False))
det.persistency.ingest_event(event_id=1, event_template="login <*>", named_variables={"user": "alice"})

data = det.export_state()   # bytes, no path given

import zipfile, io
with zipfile.ZipFile(io.BytesIO(data)) as zf:
    print(zf.namelist())

open("/tmp/demo_state.zip", "wb").write(data)

output:

['/events/1.msgpack', '/metadata.json']

unzip -l /tmp/demo_state.zip

Expected behaviour

zip file should not contains files or folders with leading slashes

Actual behaviour

zip file has files or folders with leading slashes