WebUI: replace rounding function from MooTools

The `round()` returning floating point number is not a good idea. This is due to floating point
representation is imprecise and sometimes it cannot faithfully represent a number, for example
`0.09 + 0.01 !== 0.1 `. Therefore, it should be avoided and/or utilize other function
to achieve the goal.

Also, improve `window.qBittorrent.Misc.toFixedPointString()` and add test cases.

PR #22281.

.github/workflows/ci_webui.yaml

@@ -34,7 +34,12 @@ jobs:
         run: |
           npm install
           npm ls
+          echo "::group::npm ls --all"
           npm ls --all
+          echo "::endgroup::"
+
+      - name: Run tests
+        run: npm test
 
       - name: Lint code
         run: npm run lint