process: remove usage of require('util') in `per_thread.js`

Use `require('internal/util/inspect').format` instead of
`require('util').format`.

PR-URL: https://github.com/nodejs/node/pull/26817
Refs: https://github.com/nodejs/node/issues/26546


Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>