Tdd Rust

This enforces red-green-refactor discipline for Rust filter development with real fixtures instead of synthetic test data. You capture actual command output (git log, cargo test, etc.), write failing snapshot tests with insta, implement the minimum code to pass, then verify at least 60% token reduction. It includes fallback patterns so filters never panic on malformed input, and won't let you move forward without hitting cargo fmt, clippy, and full test coverage. The workflow is opinionated about lazy_static regexes, anyhow::Result returns, and Arrange-Act-Assert structure. If you're building CLI filters and keep forgetting the savings assertions or edge cases, this keeps you honest.