test: add parser e2e fixtures

[tristanwork]

Summary

• add automated parser E2E fixture coverage for ASCII comma exports
• cover Chinese full-width comma exports and mixed comma exports with whitespace
• wire the E2E test into npm test via npm run test:e2e

Testing

• npm test

Fixes #21
Fixes #30

[tristanwork]

Local verification passes on this branch:

npm test
# parser tests: 6 passed
# parser E2E fixture tests: 4 passed

The GitHub Actions check is currently action_required with no jobs started, so it appears to need maintainer approval to run for this fork PR.