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
