Add Garak (NVIDIA LLM vulnerability scanner) parser

[Dashtid]

Description

Adds a parser for garak, NVIDIA's LLM vulnerability scanner, implementing the request in #14878 (and aligned with the AI-testing direction in discussion #13242).

The parser ingests garak's JSON Lines hit log (garak.<run_id>.hitlog.jsonl). Every line in a hit log is a detector hit, so each record becomes a Finding; hits for the same probe/target/detector are aggregated into one Finding (nb_occurences, keeping the most severe rung seen).

• Severity is derived from the detector score (0–1) and adjusted by probe family — active-attack/jailbreak families (e.g. promptinject, dan, malwaregen, xss) nudge up; content/quality families (e.g. continuation, misleading) nudge down. Note: many garak detectors emit a binary 1.0, so in practice the probe-family adjustment does most of the differentiating. Happy to tune this to maintainer preference.
• CWE is mapped from the probe family as a deliberately coarse starter, verified against MITRE: prompt-injection → CWE-1427, XSS → CWE-79, info-leak → CWE-200, default → CWE-1426 (Improper Validation of Generative AI Output).
• Prompt/output text is extracted from garak's nested Conversation/Message structures (per garak/evaluators/base.py), with fallbacks for plain-string payloads.
• Registered for hash_code deduplication on title + severity + component_name. description is intentionally excluded because garak samples the prompt/output non-deterministically per run, so including it would prevent the same weakness from deduplicating across repeated scans.

Test results

Adds unittests/tools/test_garak_parser.py covering: zero/one/many findings, the full score→severity matrix, the CWE mapping, aggregation severity-escalation (and that a later lower-scored hit does not downgrade), nested prompt/output extraction, bytes + UTF-8 BOM + non-ASCII input, and rejection of non-JSONL input. Sample hit logs are under unittests/scans/garak/.

Marked as a draft so CI can validate the full DojoTestCase suite before review.

Documentation

Adds docs/content/supported_tools/parsers/file/garak.md.

Checklist

• Submitted against dev
• Ruff-compliant (ruff.toml)
• Python 3.13 compliant
• Documentation included
• No model changes (no migration needed)
• Unit tests added
• Labels (for maintainers): suggest Import Scans and settings_changes (touches settings.dist.py for deduplication)

Closes #14878