feat: add blob reporter

[sheremet-va]

Description

For now, it's a json file with all results. If we keep it that way, then maybe we should rename the reporter.

Run vitest --reporter=blob --outputFile=reports/blob1.json to record all test runs
Run vitest --merge-reports=reports to report all test runs

TODO:

• Tests
• Docs

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.

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:.

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[AriPerkkio]

Awesome, thanks for starting the implementation for this! I've been meaninig to look into this for long time but haven't found time for it. 🙌

Some quick comments below.

[AriPerkkio]

Looks good. As test case we could have something like:

test('merge reports', async () => {
  await runVitest({
    include: ['**/first.test.ts'],
    reporters: [['blob', { outputFile: './vitest-reports/first-run.json' }]],
  })
  await runVitest({
    include: ['**/second.test.ts'],
    reporters: [['blob', { outputFile: './vitest-reports/second-run.json' }]],
  })

  const { stdout } = await runVitest({
    mergeReports: './vitest-reports',
    reporters: [['json', { outputFile: null }]], // JSON report to stdout
  })

  expect(stdout)...
})

And later we should set up an example project maybe in the vitest-tests organization demonstrating how to use --shard and mergeReports with multiple CI machines.

[hi-ogawa]

Very nice! Looks good to go after checking test and doc.