Add multi-object tracking (v0.2.0)

[fa-webai]

Summary

• Tracking: Add ByteTrack and BoT-SORT multi-object trackers with batched Kalman filter updates using native MLX operations
• CLI & Engine: Extend CLI and model engine to support track mode on video inputs
• Utilities: Add video I/O, MOT metrics, and tracker configuration files
• Packaging: Version bumped to 0.2.0; tracking dependencies (opencv-python, lap, scipy) moved to [tracking] optional extra
• Tests & Benchmarks: Comprehensive test suite and MOT17 benchmark scripts with chart generation

Changes

• 37 files changed, ~9,350 insertions
• New modules: trackers/, utils/video.py, utils/mot_metrics.py, engine/tracker.py
• Updated: cli.py, engine/model.py, engine/results.py, __init__.py, pyproject.toml, README.md
• New docs: GUIDE_TRACKING.md, CHANGELOG.md
• New CI: publish.yml workflow for PyPI releases

Test plan

• CI passes (linting + unit tests)
• Verify tracking tests pass: pytest tests/test_tracking.py tests/test_botsort.py tests/test_mot_metrics.py
• Verify CLI track command works on sample video