FEAT: Add Garak latent injection scenario

[Longhao Wang (GISWLH)]

Summary

• Add a PyRIT-native Garak latent-injection scenario covering the active upstream families (translation, report, resume, fact snippets, WHOIS, latent jailbreak).
• Store carrier contexts, injection instructions, payloads, tasks, and triggers in local datasets with family/language/provenance metadata.
• Techniques describe injection delimiter application only; exact-trigger families use `SubStringScorer`; `latent_jailbreak` is opt-in and requires a harm scorer.
• Exports, unit tests, and synchronized scanner docs (`.py` / `.ipynb`).

Testing plan

• `uv run pytest tests/unit/scenario/garak/test_latent_injection.py tests/unit/datasets/test_garak_latent_injection_dataset.py -q` (29 passed locally)

Fixes #2530