Refactored the application to improve performance, maintainability, and binary size.
Key Changes:
- **Core Algorithm**: Switched to a parallel, single-pass tree construction algorithm for O(N) traversal.
- **Architecture**: Extract core logic from `main.rs` to `lib.rs` to enable unit testing.
- **Testing**: Added comprehensive unit tests and integration tests (`tests/cli.rs`) covering CLI arguments and output formats.
- **Benchmarking**: Added `criterion` benchmarks for performance tracking.
- **Dependencies**:
- Removed `walkdir` (logic replaced by `ignore` + custom tree).
- Removed `humansize` (consolidated to `byte-unit`).
- Replaced `chrono` with lightweight `time` crate.
- Removed unused `atty`.
- **Reporting**: Optimized CSV and JSON output for correctness and zero-copy performance.
- **Documentation**: Updated CHANGELOG.md and bumped version to 0.2.0.
