Feature/persistency improvements new

[viktorbeck98]

Task

Description

Refactors stateful stability tracking so each detector can plug in its own per-value logic that survives persistence.

• Replaces the boolean expand_value flag on SingleStabilityTracker/EventStabilityTracker with a pluggable add_value_fn (detector name) + detector_config. The tracker resolves and binds the detector's add_value implementation on init and round-trips it through to_state/from_state.
• BigramFrequencyDetector: adds a custom add_value that maintains bigram frequency tables and flags low-probability character pairs; now exported from detectors/__init__.py; skip_repetitions now defaults to True; docstring/docs updated.
• CharsetDetector: custom add_value (unions characters) and matching kwargs on the auto-config persistency.
• ValueRangeDetector: custom add_value tracking min/max range; numeric casting now goes float→int; replaces exit(1) with sys.exit(1).
• .gitignore: ignore leaked local /state/ persistency dir.

How Has This Been Tested?

Adapted existing unit tests for the new add_value_fn/detector_config API (stability tracker, charset, bigram) and updated end-to-end anomaly-count assertions for the new skip_repetitions default. Ran the test suite locally.

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.