🐛 Make MLIR region moves failure-atomic

[simon1hofmann]

🤖 AI text below 🤖

Description

Makes the shared conversion moveRegion helper failure-atomic.

The helper previously moved the source region before asking the type converter
whether its block-argument signature was supported. A failed conversion therefore
left the source empty and the destination partially changed. It now computes the
signature conversion first and moves the region only after that succeeds.

This is one focused replacement for draft PR #2287 and addresses part of #2255.

Validation

• new failure-atomic regression — 1/1 passed
• full QC-to-QCO suite — 170/170 passed
• formatting, commit hooks, and git diff --check — passed

Checklist

• The pull request only contains commits that are focused and relevant to this change.
• I have added appropriate tests that cover the new/changed functionality.
• I have updated the documentation to reflect these changes.
• I have added entries to the changelog for any noteworthy additions, changes, fixes, or removals.
• I have added migration instructions to the upgrade guide (if needed).
• The changes follow the project's style guidelines and introduce no new warnings.
• The changes are fully tested and pass the CI checks.
• I have reviewed my own code changes.

If PR contains AI-assisted content:

• Any agent that created, edited, or submitted GitHub content was explicitly authorized for that scope, as required by our AI Usage Guidelines.
• Every agent-authored or agent-edited public text body begins with the visible disclosure 🤖 *AI text below* 🤖 (titles are exempt).
• I have disclosed AI assistance in the PR description.
• I confirm that I have personally reviewed and understood all AI-generated content, and accept full responsibility for it.

AI assistance disclosure: Codex extracted this focused change from the
authorized #2255 audit, validated it, and drafted this description.

[burgholzer]

This LGTM and can happily go in soon.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!