Security analysis engines for LLMTrace

This crate provides regex-based security analyzers for detecting prompt injection attacks, encoding-based attacks, role injection, PII leakage, and data leakage in LLM interactions.

Feature: ml

When the ml feature is enabled, an ML-based analyzer using the Candle framework becomes available:

• [MLSecurityAnalyzer] — runs local inference with a HuggingFace text classification model (BERT or DeBERTa v2).
• [EnsembleSecurityAnalyzer] — combines regex and ML results for higher accuracy.