Codemirror 5 to 6 upgrade (#1386)

## Launch Checklist

- Resolves #891

This PR upgrades code mirror from version 5 to version 6.
It should not change any functionality dramatically.
The filter and other expressions have line numbers now as I was not able
to remove those without introducing a lot of code, which I preferred not
to.

Before:

<img width="571" height="933" alt="image"
src="https://github.com/user-attachments/assets/02f047ee-0857-4eb1-9431-2620099ea025"
/>


After:
<img width="571" height="933" alt="image"
src="https://github.com/user-attachments/assets/7cf60155-7cd9-4c06-915e-dec2ae8247fc"
/>



 - [x] Briefly describe the changes in this PR.
 - [x] Link to related issues.
- [x] Include before/after visuals or gifs if this PR includes visual
changes.
 - [x] Write tests for all new functionality.
 - [x] Add an entry to `CHANGELOG.md` under the `## main` section.

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

.github/workflows/ci.yml

@@ -78,6 +78,20 @@ jobs:
           name: maputnik-windows
           path: ./desktop/bin/windows/
 
+  unit-tests:
+    name: "Unit tests"
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v5
+      - run: npm ci
+      - run: npm run test-unit-ci
+      - name: Upload coverage reports to Codecov
+        uses: codecov/codecov-action@v5
+        with:
+          files: ${{ github.workspace }}/coverage/coverage-final.json
+          verbose: true
+
   e2e-tests:
     name: "E2E tests using chrome"