chore: Mock getBoundingClientRect in mixed chart tests

[jperals]

Description

This is necessary for cloudscape-design/component-toolkit#165.

JSDOM does not have access to actual element dimensions and returns 0 for everything. For this reason in the mixed chart tests we are mocking window.getComputedStyle to return 2px for border width among other things. But we are not mocking HTMLElement.prototype.getBoundingClientRect, so these tests still assume that all values are 0 for the values that this function returns. Then the changes in cloudscape-design/component-toolkit#165 causes the calculated dimensions of the chart to be negative, because a non-zero border coming from window.getComputedStyle is subtracted from the zero width of the chart coming from getBoundingClientRect here (which in reality won't happen, because these calculated dimensions should include the border). And these negative dimension values causes the chart not to render expected inner elements: https://github.com/cloudscape-design/component-toolkit/actions/runs/17982007963/job/51205514110?pr=165

The solution is to add one more mock for component-toolkit's useContainerQuery, which is used by the chart to determine its width.

How has this been tested?

Ran the test with cloudscape-design/component-toolkit#165 applied to the local copy of component-toolkit. The tests only passed after the changes in this PR.

Review checklist

The following items are to be evaluated by the author(s) and the reviewer(s).

Correctness

• Changes include appropriate documentation updates.
• Changes are backward-compatible if not indicated, see CONTRIBUTING.md.
• Changes do not include unsupported browser features, see CONTRIBUTING.md.
• Changes were manually tested for accessibility, see accessibility guidelines.

Security

• If the code handles URLs: all URLs are validated through the checkSafeUrl function.

Testing

• Changes are covered with new/existing unit tests?
• Changes are covered with new/existing integration tests?

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.14%. Comparing base (74732dd) to head (b4cd748).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3894      +/-   ##
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- Coverage   97.15%   97.14%   -0.01%     
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  Files         846      846              
  Lines       24592    24592              
  Branches     8680     8680              
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- Hits        23892    23891       -1     
- Misses        693      694       +1     
  Partials        7        7              

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[jperals]

Use the same styles already in the initial render, because cloudscape-design/component-toolkit#165 applies to the initial render only.

[jperals]

Smaller widths would cause less X ticks to appear in some of the tests