Establish testing framework & CI pipeline

[aalexmmaldonado]

Description
Enhance code reliability by expanding unit and integration tests, and configure a GitHub Actions workflow. Include linting (flake8), type checking (mypy), and docs validation. Aim for high coverage and fast feedback on pull requests.

Key tasks:

• Write pytest tests for all modules, targeting ≥ 90% coverage.
• Add integration tests that cover a full parse→simulate (mock)→digest→export cycle.
• Configure GitHub Actions with separate jobs for linting, type checks, tests, and docs build.
• Display status badges in README.

Acceptance Criteria

• CI runs succeed on all checks for the main branch and pull requests.
• Coverage report indicates ≥ 90% code coverage.
• Linting and type checks report no errors.
• Tests complete within a reasonable time (e.g., < 5 minutes).