fix(ui): simplify explorer filtering + fix nested tests when search matches a suite

[hi-ogawa]

• follow-up to fix(ui): fix collapse/expand suite with file name search #11260

The explorer tree filtering had grown into several complicated layers with global ref and generator, so this PR takes on a larger cleanup to establish a simpler pipeline. While doing this, I also found a minor issue with the expand toggle during search and fixed it. See the html artifact https://gisthost.github.io/?3cbab4603b1f5c72b83b78aafc228456/vitest-pr-11262-explain-diff.html for the high-level idea of the change.

The bug shows up when a search matches a suite with nested suites. For example, searching nested failure in the fixture test/ui/fixtures/main/suite-report.test.ts should give a tree like:

_nested failure_ suite        ← search matches
  failing nested suite
    failing nested child

but on main it gives:

_nested failure_ suite        ← search matches
  failing nested suite        ← shown with no tests under it

and collapsing and expanding failing nested suite doesn't bring failing nested child back. This PR shows the full tree in both cases.

This coverage is added in e2e.

Please don't delete this checklist! Before submitting the PR, please make sure you do the following:

• It's really useful if your PR references an issue where it is discussed ahead of time. If the feature is substantial or introduces breaking changes without a discussion, PR might be closed.
• Ideally, include a test that fails without this PR but passes with it.
• Please, don't make changes to pnpm-lock.yaml unless you introduce a new test example.
• Please check Allow edits by maintainers to make review process faster. Note that this option is not available for repositories that are owned by Github organizations.

Tests

• Run the tests with pnpm test:ci.

Documentation

• If you introduce new functionality, document it. You can run documentation with pnpm run docs command.

Changesets

• Changes in changelog are generated from PR name. Please, make sure that it explains your changes in an understandable manner. Please, prefix changeset messages with feat:, fix:, perf:, docs:, or chore:.

[netlify]

✅ Deploy Preview for vitest-dev ready!

Name	Link
🔨 Latest commit	53bdaa0
🔍 Latest deploy log	https://app.netlify.com/projects/vitest-dev/deploys/6abf1d356aab9f000802a9eb
😎 Deploy Preview	https://deploy-preview-11262--vitest-dev.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.
🤖 Make changes	Run an agent on this branch

---

To edit notification comments on pull requests, go to your Netlify project configuration.