Parses unified diff output (via `parse_modified_ranges` and `run_git_diff`) into structured `FileDiff` and `RangePair` objects. Handles file creation/deletion, submodule exclusions, and context-agnostic range extraction. This module is a self-contained utility that could be reused in any Rust project needing diff analysis without importing the rest of GritQL.

Implements `ThreadedCache`, a concurrent, lock-free cache for storing file-pattern mismatch results. Uses a dedicated worker thread for background writes and atomics for lock-free reads. The pattern (delegated cache with background flushing) is reusable for any high-read, low-write caching scenario.

Provides `EmbeddedSourceMap` to map positions between an outer document (e.g., Jupyter notebook) and embedded language code blocks, supporting multi-stage edits. The generic offset-based mapping and clone-with-edits pattern can be extracted for any project that needs to track edits in embedded source regions (e.g., SQL in Python, HTML in JS).

Defines the `Messager` trait and several implementations (`JSONLineMessenger`, `TestingMessenger`, `RemoteMessenger`) for structured output of pattern match results, progress, and diagnostics. The trait separates result emission from processing logic and supports progress bars, summary formatting, and interactive prompts. This pattern is reusable for any tool needing pluggable output formats (JSON, human-readable, remote).