feat: use more compact default Debug format

[kanru]

Removes the empty line between errors and use box-drawing characters for compact rendering.

[Copilot]

Pull request overview

This PR updates exn’s default Debug formatting to render error trees more compactly by removing the extra blank separator line and switching to box-drawing characters.

Changes:

• Update write_exn to print child frames using ├── / └── connectors and │ indentation.
• Refresh Insta snapshots to match the new compact Debug output across linear and tree-shaped error graphs.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
exn/src/debug.rs	Changes the Debug tree rendering to use box-drawing connectors and removes the extra separator line.
exn/tests/snapshots/main__tree_error.snap	Updates expected tree-shaped debug output to new connector style.
exn/tests/snapshots/main__linear_error.snap	Updates expected linear-chain debug output to new connector style.
exn/tests/snapshots/main__result_ext.snap	Updates expected debug output for ResultExt case.
exn/tests/snapshots/main__new_with_source.snap	Updates expected debug output for Exn::new with source.

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[kanru]

I see, there are snapshot tests in the example. I'll fix those too.

[andylokandy]

Thanks for the update. Could you rebase this onto the latest main, resolve the conflict, and refresh the tests?

Looks like maintainers cannot push to this branch directly, so we'll need your help with the update.

[andylokandy]

@kanru Thank you!