chore(release): bump version to 1.3.18

Bump the package version to 1.3.18, upgrade dependencies,
consolidate module exports, add a unit test suite, and document
all changes.

- Bump package version to 1.3.18 in pyproject.toml
- Upgrade pydantic-settings to 2.14.2 and pyright to 1.1.411
- Consolidate package exports in mdrsclient/__init__.py
- Add a comprehensive unit test suite in tests/test_commands.py
- Document testing execution and add full history in CHANGELOG.md

README.md

@@ -236,3 +236,15 @@ client.upload("/path/to/local/data", "neurodata:/NIU/Repository/TEST/", is_recur
 client.download("neurodata:/NIU/Repository/TEST/data", "/path/to/local", is_recursive=True)
 ```
 
+## Testing
+
+You can run the unit test suite using the standard library `unittest` discover runner:
+
+```shell
+.venv/bin/python -m unittest discover tests
+```
+
+## Changelog
+
+See [CHANGELOG.md](./CHANGELOG.md) for the full change history.
+