Migrate CI/CD to GitHub Actions and add coverage reporting

[RadValentin]

Overview

Currently using CircleCI for CI/CD, but we should migrate to GitHub Actions for simpler management and better GitHub integration. Additionally, code coverage is generated locally but not published anywhere.

Objectives

• Migrate CI/CD pipeline from CircleCI to GitHub Actions
• Publish code coverage reports to a coverage service (e.g., Codecov)
• Retire CircleCI configuration

Tasks

Migrate to GitHub Actions

• Create .github/workflows/test.yml workflow that:
  • Runs tests with Node.js 22.22.1 (matching current CircleCI config)
  • Executes npm run test-cov to generate coverage reports
  • Uses mocha-junit-reporter for test results
  • Publishes test results to GitHub

Add Coverage Reporting

• Integrate with Codecov or similar service
• Add workflow step to upload coverage reports
• Configure necessary secrets (Codecov token, etc.)
• Add coverage badge to README.md

Cleanup

• Remove .circleci/config.yml
• Verify workflow runs successfully on next commit
• Update CONTRIBUTE.md if it references CircleCI

Acceptance Criteria

• GitHub Actions workflow successfully runs on every push
• Code coverage reports are published and visible
• No CircleCI configuration remains
• All checks pass (tests, linting, type checking)