want to have Resolution Unit

[tictaqqn]

Hi Imagemagick returns resolution with both unit PixcelsPerInch and PixcelsPerCentimeter and gm.res returns different unit of values, so I want this gm library to return Resolution Unit, too.

ex)

$ identify -verbose resolution.png | grep 'Resolution\|Units'
  Resolution: 118.11x118.11
  Units: PixelsPerCentimeter
$ identify -verbose resolution.jpg | grep 'Resolution\|Units'
  Resolution: 300x300
  Units: PixelsPerInch

and in gm

const GM = gm.subClass({ imageMagick: true })
export function getResolution(buf: Buffer): Promise<string | undefined> {
  return new Promise((resolve, reject) => {
    GM(buf).res((err, value: string | undefined) => {
      if (err) {
        reject(err)
        return
      }
      resolve(value)
    })
  })
}
const buf = await fs.promises.readFile('test/assets/resolution.png')
const res = await getResolution(buf) // = '118.11x118,11' in PixelsPerCentimeter
////
const buf = await fs.promises.readFile('test/assets/resolution.jpg')
const res = await getResolution(buf) // '300x300' in PixelsPerInch