fix(editor): make fold all reliable for large files

[bajrangCoder]

No description provided.

[greptile-apps]

Confidence Score: 5/5

The PR appears safe to merge, with the previously requested progressive-path and cancellation coverage now present.

Findings

1.  Progressive Path Lacks Coverage ▶

Summary

This PR makes “Fold all” complete large-file parsing incrementally during idle periods before applying all discovered folds.

• Adds cancellable, progressive parsing with bounded idle-time budgets.
• Cancels pending folding when the document changes or “Unfold all” runs.
• Collects syntax and fold-service ranges into one ordered transaction.
• Adds unit coverage for multi-slice completion and cancellation behavior.

_{Reviews (2) · Last reviewed commit: "Merge branch 'fix/fold-all-large-files' ..."}