test: Improve screenshot test pages for select + multiselect

[SpyZzey]

Description

This improves the dev pages in select + multiselect to have some padding for the screenshot tests as well as a virtual scroll button to toggle and test differences in virtual scroll and normal mode.

Related links, issue #, if available: n/a

How has this been tested?

Manual testing.

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 (42be1aa) to head (fa51509).
⚠️ Report is 6 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4179   +/-   ##
=======================================
  Coverage   97.14%   97.14%           
=======================================
  Files         873      873           
  Lines       25653    25653           
  Branches     9284     9283    -1     
=======================================
  Hits        24921    24921           
- Misses        685      726   +41     
+ Partials       47        6   -41     

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[Copilot]

Pull request overview

This PR improves the screenshot test pages for select and multiselect components by adding padding to the screenshot area and introducing a toggle button to test virtual scroll functionality.

Changes:

• Added virtual scroll toggle button to both select and multiselect custom render option pages
• Added padding to screenshot areas for better visual testing
• Updated container styles to use maxInlineSize and added blockSize for better layout control

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
pages/select/custom-render-option.page.tsx	Added virtual scroll toggle functionality and improved screenshot area styling with padding and fixed dimensions
pages/multiselect/custom-render-option.page.tsx	Added virtual scroll toggle functionality and improved screenshot area styling with padding and fixed dimensions

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