refactor: minimal improvements to docs, testing, and utilities

[Dark-Brain07]

Description

This PR addresses several small but meaningful improvements to the repository, focusing on developer experience, documentation, and code quality.

Changes

1. Documentation:

   • Added CONTRIBUTING.md to guide new contributors.
   • Updated README.md to link to the contributing guide.
   • Expanded docstrings in src/roma_dspy/core/__init__.py.

2. Utilities:

   • Added get_missing_features() to src/roma_dspy/utils/lazy_imports.py to help users identify which optional dependencies are missing.
   • Improved type hinting and docstrings in lazy_imports.py.

3. Testing & CI:

   • Added a new unit test file tests/unit/test_lazy_imports.py to cover the utility functions.
   • Added a GitHub Actions workflow .github/workflows/test.yml to run tests on push and PR.

4. Metadata:

   • Added keywords to pyproject.toml to improve PyPI discoverability.

Verification

• Added new unit tests pass.
• Verified that lazy_imports functionality remains intact.
• Documentation renders correctly.