[test] Clean up component tests

[atomiks]

This PR does a mechanical cleanup pass over component tests

Changes

• Add missing test files for component parts that need their own suites.
• Normalize describe grouping and prop, Field, and Form sections.
• Rename unclear tests and remove stale waits, skips, and imports where safe.

[pkg-pr-new]

• base-ui-tanstack-start

• vite-css-base-ui-example

  pnpm add https://pkg.pr.new/mui/base-ui/@base-ui/react@4842
  

  pnpm add https://pkg.pr.new/mui/base-ui/@base-ui/utils@4842
  

commit: f8ebbbd

[code-infra-dashboard]

Bundle size

Bundle	Parsed size	Gzip size
@base-ui/react	0B(0.00%)	0B(0.00%)

Details of bundle changes

Performance

Total duration: 1,286.91 ms +66.88 ms^(+5.5%) | Renders: 50 ⁽⁺⁰⁾ | Paint: 1,957.60 ms +72.06 ms^(+3.8%)

Test	Duration	Renders
Popover mount (300 instances)	76.68 ms 🔺+12.82 ms(+20.1%)	1 (+0)
Dialog mount (300 instances)	64.42 ms 🔺+12.72 ms(+24.6%)	1 (+0)

10 tests within noise — details

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