docs: add bench test case `TaskResult` type description

[btea]

Description

Add TaskResult field information description in the documentation.

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[hi-ogawa]

It looks a bit noisy to show this for each re-run :thinking: Would it be fine if we mention that in the doc? https://vitest.dev/guide/features.html#benchmarking or https://vitest.dev/api/#bench

[btea]

Of course, it would be better to add this to the documentation. However, I think it might be more convenient and quicker to output this in the terminal so that it can be directly accessed.

Maybe we can add it on both sides. As for what you said, it will be a bit noisy when it is printed every time it is re-run. Maybe we can add a shortcut key to print this information when the corresponding key is pressed. What do you think?

[sheremet-va]

If we provide an API to run benchmarks, the API should be documented in https://vitest.dev

Ref: https://github.com/vitest-dev/vitest/issues/279

[btea]

Thanks for the link, I have updated the document.