[feat] diff based analysis

[joshbouncesecurity]

This project gave me a great idea:

• https://securitydepth.hashnode.dev/diffguard-llm-powered-security-review-for-staged-git-diffs#bugs-found-along-the-way
• https://github.com/nick79/diffguard

Instead of taking units from the whole codebase and looking at reachability, can you just take units that are modified by a diff and then scan those to perform an incremental scan?