feat: detect trust_remote_code model loading

[ynachiket]

Summary

• add AI206 to flag Hugging Face from_pretrained(..., trust_remote_code=True) model loading
• add targeted tests for the rule metadata, matcher behavior, and scanner integration when the Rust core is available

Closes #18

Validation

• /tmp/pyspector-pdlc043-venv/bin/python -m pytest tests/unit/test_ai_rules.py -q -> 2 passed, 2 skipped locally because the PySpector Rust core is not available in this runner
• /tmp/pyspector-pdlc043-venv/bin/python -m py_compile tests/unit/test_ai_rules.py
• TOML parse check for src/pyspector/rules/built-in-rules-ai.toml
• direct AST matcher shape check for trust_remote_code=True vs False
• git diff --check

[ParzivalHack]

Hey @ynachiket, thanks for opening your first PR, we appreciate the contribution! This new rule is a great addition to our current ruleset. I tested it locally and it works great on my end. I require no further edits, merging :)