feat(benchmark)!: rewrite the public API

[sheremet-va]

Related #7850

New API as part of the test instead of being a test:

import { expect, test } from 'vitest'

test('compare JSON libraries', async ({ bench }) => {
  const input = '{"key":"value","nested":{"a":1}}'

  const result = await bench.compare(
    bench('JSON.parse', () => {
      JSON.parse(input)
    }),
    bench('custom parser', () => {
      customParse(input)
    }),
  )
})

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[hi-ogawa]

did surface level check. the api looks good.
will read new part of implementation nexy later.

[hi-ogawa]

lgtm! left minor reviews.