Add Code Coverage Reporting to CI

[Carrington-dev]

Description

Tests run in CI but no coverage reporting, making it hard to identify untested code.

Tasks

• Add pytest-cov to test dependencies
• Configure coverage in CI workflow
• Upload coverage to Codecov or Coveralls
• Add coverage badge to README
• Set minimum coverage threshold
• Block PRs that decrease coverage

Implementation

# .github/workflows/test-dj-payfast.yml
- name: Test with pytest and coverage
  run: |
    pytest --cov=payfast --cov-report=xml --cov-report=html

- name: Upload coverage to Codecov
  uses: codecov/codecov-action@v3
  with:
    file: ./coverage.xml
    fail_ci_if_error: true
    flags: unittests

- name: Check coverage threshold
  run: |
    coverage report --fail-under=80

Acceptance Criteria

• Coverage calculated in CI
• Coverage badge in README
• PRs show coverage changes
• Minimum threshold enforced