ci: add GitHub Actions workflows and modernize packaging

[juno-rmks]

Summary

Improve CI/CD, packaging configuration, and project documentation.

This PR mainly focuses on development workflow improvements and
packaging modernization ahead of the next release.

Changes

CI / CD

• Add GitHub Actions CI workflow
• Add release workflow for publishing to TestPyPI and PyPI

Packaging

• Simplify build-system configuration in pyproject.toml
• Update packaging configuration to follow current setuptools practices
• Reorganize development dependencies into test, docs, and dev extras

Documentation

• Improve documentation structure and consistency
• Update CLI help text and related docstrings
• Update README and documentation pages

Lint / Formatting

• Adjust pylint configuration for converter design patterns
• Exclude docs/source/conf.py from Black and isort checks

Tests

• Fix Windows test failures caused by platform default encoding in CLI file tests

Notes

This release is published as a release candidate to TestPyPI
to verify the packaging and release workflow before the final release.