ruff server: Important errors are now shown as popups

[snowsignal]

Summary

Fixes #10866.

Introduces the show_err_msg! macro which will send a message to be shown as a popup to the client via the window/showMessage LSP method.

Test Plan

Insert various show_err_msg! calls in common code paths (for example, at the beginning of event_loop) and confirm that these messages appear in your editor.

To test that panicking works correctly, add this to the top of the fn run definition in crates/ruff_server/src/server/api/requests/execute_command.rs:

panic!("This should appear");

Then, try running a command like Ruff: Format document from the command palette (Ctrl/Cmd+Shift+P). You should see the following messages appear:

[MichaReiser]

Having to call both tracing::error and show_err_msg! is a bit verbose but I could see why it is needed. I think my main challenge as a developer would be is to know where I need to use what (not all tracing sides have a show_err_msg call but all show_err_msg calls have a tracing::error call).

[github-actions]

ruff-ecosystem results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

✅ ecosystem check detected no linter changes.

[MichaReiser]

The code looks good.

To me it's still unclear when to use show_err_msg and tracing:error and why/when I need to use both

Having to call both tracing::error and show_err_msg! is a bit verbose but I could see why it is needed. I think my main challenge as a developer would be is to know where I need to use what (not all tracing sides have a show_err_msg call but all show_err_msg calls have a tracing::error call).

[snowsignal]

To me it's still unclear when to use show_err_msg and tracing:error and why/when I need to use both

show_err_msg shows a visible popup in the editor, with a user-friendly message. tracing::error is for logging errors in the Output window, usually in a more verbose and technical message.

Not all errors need to be surfaced to the user as visibly as a popup, which is why only some of the error logs also show a message to the user.