`charset` function

Would be cool to have a charset function from mime-types:

const EXTRACT_TYPE_REGEXP = /^\s*([^;\s]*)(?:;|\s|$)/
const TEXT_TYPE_REGEXP = /^text\//i

export function charset (type) {
  if (!type || typeof type !== 'string') return false
  const match = EXTRACT_TYPE_REGEXP.exec(type)
  const mime = match && db[match[1].toLowerCase()]

  if (mime && mime.charset) return mime.charset

  // default text/* to utf-8
  if (match && TEXT_TYPE_REGEXP.test(match[1])) return 'UTF-8'

  return false
}

https://github.com/jshttp/mime-types/blob/c6ff9b224577f0cd49f1155f421b24c24a57bc3e/index.js#L49-L68

Start by reviewing the linked mime-types implementation and inspect mrmime's existing exports and tests to find the appropriate entry point. Add the requested charset function with the shown handling for invalid input, MIME database matches, and text/* defaults, then verify its behavior alongside the existing utility tests.