fix: raise ValidationError for empty OpenQASM loads()

[tonycoder-hub]

Summary of changes

openqasm3.parse("") (and whitespace-only input) raises AttributeError ('NoneType' object has no attribute 'line') instead of QASM3ParsingError. pyqasm.loads() only caught QASM3ParsingError, so empty strings bubbled up as an unexpected AttributeError.

This PR also catches AttributeError from openqasm3.parse and maps it to ValidationError, matching other unparseable-string failures. Header-only programs (OPENQASM 3.0;\n) still load successfully.

Fixes #437

[argus-eye]

Argus review

Auto-review is off for this repo. Tick the box below to run a review on this PR.

• Trigger Argus review

Estimated cost

• Files changed: 2
• Diff lines (±): 18
• Historical avg: ~350.7k tokens · ~$1.38 · across last 13 review(s)

Tip: you can also comment @argus-eye review at any time.

[coderabbitai]

Important

Review skipped

Auto reviews are disabled on this repository. Please check the settings in the CodeRabbit UI or the .coderabbit.yaml file in this repository. To trigger a single review, invoke the @coderabbitai review command.

⚙️ Run configuration

• Configuration used: Repository: qBraid/pyqasm/.coderabbit.yaml
• Review profile: CHILL
• Plan: Advanced
• Run ID: eb28d3ba-b225-4353-9bea-864b2e7cfcf8

---

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

Use the checkbox below for a quick retry:

• 🔍 Trigger review

• Autofix · Keep fixing CodeRabbit findings and required CI, and resolving merge conflicts

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

---

_{Comment @coderabbitai help to get the list of available commands.}

[TheGupta2012]

Hi @tonycoder-hub , thanks for fixing this! The changes lgtm. Can you please fix the format job in CI and add a CHANGELOG entry? Should be good to merge post that

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[tonycoder-hub]

Thanks @TheGupta2012 — format (trailing newlines) is fixed and I've added a CHANGELOG.md Unreleased Fixed entry for this PR. Please take another look when you have a moment.