Add unit test

[nwaughachukwuma]

Summary

This PR modernizes seewav by adding continuous-integration, full type-hints, stricter unit-testing and a clearer, more ergonomic CLI/API.

---

✨ Key Features & Improvements

1. GitHub Actions CI

   • Runs the test-suite on Python 3.9 → 3.12
   • Includes pytest-cov; uploads an XML coverage artefact

2. 100% Type-annotated Public API

   • All public helpers in seewav.py now have explicit PEP-484 annotations
   • New meta-test (tests/test_signatures.py) fails the build if a public function lacks annotations

3. Unified Size Handling

   • New --size WxH CLI flag (e.g. --size 640x360)
   • Existing -W/--width and -H/--height remain with defaults (480 × 300); --size overrides them
   • Library call continues to accept the size=(w, h) tuple

4. Robust Argument Validation

   • Added seewav.parse_size_token helper
   • Expanded test-suite (tests/test_arguments.py) checks:
     • parse_size_token – valid & invalid paths
     • parse_color – valid & invalid RGB strings
     • read_audio – fails gracefully on non-audio files
     • visualize – detects channel/--stereo mismatches
   • Test count increased from 9 → 27; all green

5. Documentation Updates

   • README gains a "Library usage & type-safety" section and updated option table:

     --size WxH            Output video dimension (e.g. 640x360)
     -W, --width WIDTH     Width in pixels (default 480)
     -H, --height HEIGHT   Height in pixels (default 300)
     

   • Example snippet for programmatic use with size=(640, 360)

---

🛠️ Implementation Notes

• CI Workflow — .github/workflows/ci.yml
  • Installs minimal deps (numpy, tqdm, pytest, pytest-cov) and optional ffmpeg
• Helper Functions
  • parse_size_token(token: str) -> tuple[int, int]
  • Improved error messages via fatal()
• Backward Compatibility
  • Width/height flags preserved; no breaking change for existing users
• Coverage
  • .coveragerc excludes tests/venv; --cov-report=term-missing --cov-report=xml in CI

---

🔍 How to Review

1. API surface – inspect new/changed functions & type-hints in seewav.py
2. CLI behaviour – run:

seewav --size 800x450 in.wav out.mp4
seewav -W 800 -H 450 in.wav out.mp4 # still works

3. Tests – execute pytest -vv locally; 27 tests including argument-validation and meta type-checking should pass
4. CI – confirm new workflow passes on all Pythons

---

This PR brings the project up to date with modern Python best-practices, increases test coverage, and lays the groundwork for future features with confidence in correctness.

Co-author: OpenAI o3 model via Codex CLI

[nwaughachukwuma]

cc @adefossez