Test linting behavior in integration (close to real world)

[nikku]

Proposed Changes

We previously did not test editor linting behavior during value changes. We also did not use the standard "batteries included" by codemirror, but took a (faster) shortcut to force linting. That works "for tests", but does not verify actual user behavior.

This PR adds some real-world tests, to validate linting works as expected across the use-cases we cover.

Checklist

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  • Link to related issue(s), i.e. Closes {LINK_TO_ISSUE} or Related to {LINK_TO_ISSUE}
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  • Steps to try out, i.e. using the @bpmn-io/sr tool

[Copilot]

Pull request overview

This PR aims to test CodeMirror linting behavior in a more integration-like (“real user”) way, validating that linting triggers correctly on initial render and after value updates.

Changes:

• Update lint-related tests to assert on actual diagnostics arrays and add integration-style lint trigger tests.
• Introduce a lint event on FeelEditor (backed by a new mitt event emitter) and wire existing onLint through it.
• Bump several CodeMirror dependencies, add mitt, and replace karma-chrome-launcher with karma-chrome-launcher-2.

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 4 comments.

File	Description
test/spec/CodeEditor.spec.js	Updates lint assertions to use diagnostics arrays; adds integration-style tests for lint triggering and new lint helpers.
src/index.js	Adds an internal event emitter and exposes on/off; emits lint events and forwards them to the existing onLint callback.
package.json	Updates dependencies (CodeMirror patches), adds mitt, and switches to karma-chrome-launcher-2.
package-lock.json	Locks updated dependency graph reflecting the package.json changes.

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[barmac]

LGTM

[barmac]

Released in v2.4.0. I also updated the readme to reflect new API: https://github.com/bpmn-io/feel-editor?tab=readme-ov-file#events