chore: allow dompdf 2 for downstream compatibility

[vitormattos]

📝 Summary

Broaden the dompdf/dompdf requirement to allow both ^2.0 and ^3.0.

This keeps the package compatible with downstream consumers that still need the Dompdf 2 / Sabberworm 8 runtime combination, while preserving support for newer installations on Dompdf 3.

🧪 How to test

1. Run composer validate --no-check-publish.
2. Confirm composer.json accepts both dompdf 2.x and 3.x.
3. Confirm existing lock/install on Dompdf 3 remains valid.

⚙️ API / Back-end changes

• Broaden dompdf/dompdf compatibility from ^3.0 to ^2.0 || ^3.0
• Unit and/or integration tests added – required for backend changes
• Documentation updated (if applicable)

✅ Checklist

• I have read and followed the contribution guide.
• All existing tests pass.
• New tests cover the changed behaviour.
• Commit messages follow Conventional Commits.
• Commits are signed off (git commit -s).

🤖 AI (if applicable)

• The content of this PR was partially or fully generated using AI.